Rules with anssi Reference in Guide to the Secure Configuration of Oracle Linux 7


Reference (anssi) Rule Title Description Rationale Variable Setting
BP28(R1) Uninstall the telnet server The telnet daemon should be uninstalled. telnet allows clear text communications, and does not protect any data transmission between client and server. Any confidential data can be listened and no integrity checking is made.'
BP28(R1) Uninstall DHCP Server Package If the system does not need to act as a DHCP server, the dhcp package can be uninstalled. The dhcp package can be removed with the following command: 
$ sudo yum erase dhcp
 Removing the DHCP server ensures that it cannot be easily or accidentally reactivated and disrupt network operation.
BP28(R1) Uninstall Sendmail Package Sendmail is not the default mail transfer agent and is not installed by default. The sendmail package can be removed with the following command: 
$ sudo yum erase sendmail
 The sendmail software was not developed with security in mind and its design prevents it from being effectively contained by SELinux. Postfix should be used instead.
BP28(R1) Uninstall xinetd Package The xinetd package can be removed with the following command: 
$ sudo yum erase xinetd
 Removing the xinetd package decreases the risk of the xinetd service's accidental (or intentional) activation.
BP28(R1) Remove NIS Client The Network Information Service (NIS), formerly known as Yellow Pages, is a client-server directory service protocol used to distribute system configuration files. The NIS client (ypbind) was used to bind a system to an NIS server and receive the distributed configuration files. The NIS service is inherently an insecure system that has been vulnerable to DOS attacks, buffer overflows and has poor authentication for querying NIS maps. NIS generally has been replaced by such protocols as Lightweight Directory Access Protocol (LDAP). It is recommended that the service be removed.
BP28(R1) Uninstall ypserv Package The ypserv package can be removed with the following command: 
$ sudo yum erase ypserv
 The NIS service provides an unencrypted authentication service which does not provide for the confidentiality and integrity of user passwords or the remote session. Removing the ypserv package decreases the risk of the accidental (or intentional) activation of NIS or NIS+ services.
BP28(R1) Uninstall rsh Package The rsh package contains the client commands for the rsh services These legacy clients contain numerous security exposures and have been replaced with the more secure SSH package. Even if the server is removed, it is best to ensure the clients are also removed to prevent users from inadvertently attempting to use these commands and therefore exposing their credentials. Note that removing the rsh package removes the clients for rsh,rcp, and rlogin.
BP28(R1) Uninstall rsh-server Package The rsh-server package can be removed with the following command: 
$ sudo yum erase rsh-server
 The rsh-server service provides unencrypted remote access service which does not provide for the confidentiality and integrity of user passwords or the remote session and has very weak authentication. If a privileged user were to login using this service, the privileged user password could be compromised. The rsh-server package provides several obsolete and insecure network services. Removing it decreases the risk of those services' accidental (or intentional) activation.
BP28(R1) Uninstall talk Package The talk package contains the client program for the Internet talk protocol, which allows the user to chat with other users on different systems. Talk is a communication program which copies lines from one terminal to the terminal of another user. The talk package can be removed with the following command: 
$ sudo yum erase talk
 The talk software presents a security risk as it uses unencrypted protocols for communications. Removing the talk package decreases the risk of the accidental (or intentional) activation of talk client program.
BP28(R1) Uninstall talk-server Package The talk-server package can be removed with the following command: 
 $ sudo yum erase talk-server
 The talk software presents a security risk as it uses unencrypted protocols for communications. Removing the talk-server package decreases the risk of the accidental (or intentional) activation of talk services.
BP28(R1) Remove telnet Clients The telnet client allows users to start connections to other systems via the telnet protocol. The telnet protocol is insecure and unencrypted. The use of an unencrypted transmission medium could allow an unauthorized user to steal credentials. The ssh package provides an encrypted session and stronger security and is included in Oracle Linux 7.
BP28(R1) Uninstall telnet-server Package The telnet-server package can be removed with the following command: 
$ sudo yum erase telnet-server
 It is detrimental for operating systems to provide, or install by default, functionality exceeding requirements or mission objectives. These unnecessary capabilities are often overlooked and therefore may remain unsecure. They increase the risk to the platform by providing additional attack vectors.
The telnet service provides an unencrypted remote access service which does not provide for the confidentiality and integrity of user passwords or the remote session. If a privileged user were to login using this service, the privileged user password could be compromised.
Removing the telnet-server package decreases the risk of the telnet service's accidental (or intentional) activation.
BP28(R1) Uninstall tftp-server Package The tftp-server package can be removed with the following command: 
 $ sudo yum erase tftp-server
 Removing the tftp-server package decreases the risk of the accidental (or intentional) activation of tftp services.

If TFTP is required for operational support (such as transmission of router configurations), its use must be documented with the Information Systems Securty Manager (ISSM), restricted to only authorized personnel, and have access control rules established.
BP28(R4) Ensure SELinux State is Enforcing The SELinux state should be set to at system boot time. In the file /etc/selinux/config, add or correct the following line to configure the system to boot into enforcing mode: 
SELINUX=
 Setting the SELinux state to enforcing ensures SELinux is able to confine potentially compromised processes to the security policy, which is designed to prevent them from causing damage to the system or further elevating their privileges.
BP28(R5) Ensure Users Re-Authenticate for Privilege Escalation - sudo !authenticate The sudo !authenticate option, when specified, allows a user to execute commands using sudo without having to authenticate. This should be disabled by making sure that the !authenticate option does not exist in /etc/sudoers configuration file or any sudo configuration snippets in /etc/sudoers.d/. Without re-authentication, users may access resources or perform tasks for which they do not have authorization.

When operating systems provide the capability to escalate a functional capability, it is critical that the user re-authenticate.
BP28(R5) Ensure Users Re-Authenticate for Privilege Escalation - sudo NOPASSWD The sudo NOPASSWD tag, when specified, allows a user to execute commands using sudo without having to authenticate. This should be disabled by making sure that the NOPASSWD tag does not exist in /etc/sudoers configuration file or any sudo configuration snippets in /etc/sudoers.d/. Without re-authentication, users may access resources or perform tasks for which they do not have authorization.

When operating systems provide the capability to escalate a functional capability, it is critical that the user re-authenticate.
BP28(R5) Ensure rsyslog is Installed Rsyslog is installed by default. The rsyslog package can be installed with the following command: 
 $ sudo yum install rsyslog
 The rsyslog package provides the rsyslog daemon, which provides system logging services.
BP28(R5) Enable rsyslog Service The rsyslog service provides syslog-style logging by default on Oracle Linux 7. The rsyslog service can be enabled with the following command: 
$ sudo systemctl enable rsyslog.service
 The rsyslog service must be running in order to provide logging services, which are essential to system administration.
BP28(R5) Ensure Log Files Are Owned By Appropriate Group The group-owner of all log files written by rsyslog should be . These log files are determined by the second part of each Rule line in /etc/rsyslog.conf and typically all appear in /var/log. For each log file LOGFILE referenced in /etc/rsyslog.conf, run the following command to inspect the file's group owner: 
$ ls -l LOGFILE
If the owner is not , run the following command to correct this: 
$ sudo chgrp  LOGFILE
 The log files generated by rsyslog contain valuable information regarding system configuration, user authentication, and other such information. Log files should be protected from unauthorized access.
BP28(R5) Ensure Log Files Are Owned By Appropriate User The owner of all log files written by rsyslog should be . These log files are determined by the second part of each Rule line in /etc/rsyslog.conf and typically all appear in /var/log. For each log file LOGFILE referenced in /etc/rsyslog.conf, run the following command to inspect the file's owner: 
$ ls -l LOGFILE
If the owner is not , run the following command to correct this: 
$ sudo chown  LOGFILE
 The log files generated by rsyslog contain valuable information regarding system configuration, user authentication, and other such information. Log files should be protected from unauthorized access.
BP28(R5) Ensure syslog-ng is Installed syslog-ng can be installed in replacement of rsyslog. The syslog-ng-core package can be installed with the following command: 
$ sudo yum install syslog-ng-core
 The syslog-ng-core package provides the syslog-ng daemon, which provides system logging services.
BP28(R5) Enable syslog-ng Service The syslog-ng service (in replacement of rsyslog) provides syslog-style logging by default on Debian. The syslog-ng service can be enabled with the following command: 
$ sudo systemctl enable syslog-ng.service
 The syslog-ng service must be running in order to provide logging services, which are essential to system administration.
BP28(R7) Ensure Logs Sent To Remote Host To configure rsyslog to send logs to a remote log server, open /etc/rsyslog.conf and read and understand the last section of the file, which describes the multiple directives necessary to activate remote logging. Along with these other directives, the system can be configured to forward its logs to a particular log server by adding or correcting one of the following lines, substituting appropriately. The choice of protocol depends on the environment of the system; although TCP and RELP provide more reliable message delivery, they may not be supported in all environments.
To use UDP for log message delivery: 
*.* @

To use TCP for log message delivery: 
*.* @@

To use RELP for log message delivery: 
*.* :omrelp:

There must be a resolvable DNS CNAME or Alias record set to "" for logs to be sent correctly to the centralized logging utility.		 A log server (loghost) receives syslog messages from one or more systems. This data can be used as an additional log source in the event a system is compromised and its local logs are suspect. Forwarding log messages to a remote loghost also provides system administrators with a centralized place to view the status of multiple hosts within the enterprise.
BP28(R08) Ensure Software Patches Installed If the system is joined to the ULN or a yum server, run the following command to install updates: 
$ sudo yum update
If the system is not configured to use one of these sources, updates (in the form of RPM packages) can be manually downloaded from the ULN and installed using rpm.

NOTE: U.S. Defense systems are required to be patched within 30 days or sooner as local policy dictates.		 Installing software updates is a fundamental mitigation against the exploitation of publicly-known vulnerabilities. If the most recent security patches and updates are not installed, unauthorized users may take advantage of weaknesses in the unpatched software. The lack of prompt attention to patching could result in a system compromise.
BP28(R9) Enable NX or XD Support in the BIOS Reboot the system and enter the BIOS or Setup configuration menu. Navigate the BIOS configuration menu and make sure that the option is enabled. The setting may be located under a Security section. Look for Execute Disable (XD) on Intel-based systems and No Execute (NX) on AMD-based systems. Computers with the ability to prevent this type of code execution frequently put an option in the BIOS that will allow users to turn the feature on or off at will.
BP28(R9) Install PAE Kernel on Supported 32-bit x86 Systems Systems that are using the 64-bit x86 kernel package do not need to install the kernel-PAE package because the 64-bit x86 kernel already includes this support. However, if the system is 32-bit and also supports the PAE and NX features as determined in the previous section, the kernel-PAE package should be installed to enable XD or NX support. The kernel-PAE package can be installed with the following command: 
$ sudo yum install kernel-PAE
The installation process should also have configured the bootloader to load the new kernel at boot. Verify this after reboot and modify /etc/default/grub if necessary.		 On 32-bit systems that support the XD or NX bit, the vendor-supplied PAE kernel is required to enable either Execute Disable (XD) or No Execute (NX) support.
BP28(R10) Prefer to use a 64-bit Operating System when supported Prefer installation of 64-bit operating systems when the CPU supports it. Use of a 64-bit operating system offers a few advantages, like a larger address space range for Address Space Layout Randomization (ASLR) and systematic presence of No eXecute and Execute Disable (NX/XD) protection bits.
BP28(R11) IOMMU configuration directive On x86 architecture supporting VT-d, the IOMMU manages the access control policy between the hardware devices and some of the system critical units such as the memory. On x86 architectures, activating the I/OMMU prevents the system from arbritrary accesses potentially made by hardware devices.
BP28(R12) Ensure /boot Located On Separate Partition It is recommended that the /boot directory resides on a separate partition. This makes it easier to apply restrictions e.g. through the noexec mount option. Eventually, the /boot partition can be configured not to be mounted automatically with the noauto mount option. The /boot partition contains the kernel and bootloader files. Access to this partition should be restricted.
BP28(R12) Ensure /home Located On Separate Partition If user home directories will be stored locally, create a separate partition for /home at installation time (or migrate it later using LVM). If /home will be mounted from another system such as an NFS server, then creating a separate partition is not necessary at installation time, and the mountpoint can instead be configured later. Ensuring that /home is mounted on its own partition enables the setting of more restrictive mount options, and also helps ensure that users cannot trivially fill partitions used for log or audit data storage.
BP28(R12) Ensure /opt Located On Separate Partition It is recommended that the /opt directory resides on a separate partition. The /opt partition contains additional software, usually installed outside the packaging system. Putting this directory on a separate partition makes it easier to apply restrictions e.g. through the nosuid mount option.
BP28(R12) Ensure /srv Located On Separate Partition If a file server (FTP, TFTP...) is hosted locally, create a separate partition for /srv at installation time (or migrate it later using LVM). If /srv will be mounted from another system such as an NFS server, then creating a separate partition is not necessary at installation time, and the mountpoint can instead be configured later. Srv deserves files for local network file server such as FTP. Ensuring that /srv is mounted on its own partition enables the setting of more restrictive mount options, and also helps ensure that users cannot trivially fill partitions used for log or audit data storage.
BP28(R12) Ensure /tmp Located On Separate Partition The /tmp directory is a world-writable directory used for temporary file storage. Ensure it has its own partition or logical volume at installation time, or migrate it using LVM. The /tmp partition is used as temporary storage by many programs. Placing /tmp in its own partition enables the setting of more restrictive mount options, which can help protect programs which use it.
BP28(R12) Ensure /usr Located On Separate Partition It is recommended that the /usr directory resides on a separate partition. The /usr partition contains system software, utilities and files. Putting it on a separate partition allows limiting its size and applying restrictions through mount options.
BP28(R12) Ensure /var Located On Separate Partition The /var directory is used by daemons and other system services to store frequently-changing data. Ensure that /var has its own partition or logical volume at installation time, or migrate it using LVM. Ensuring that /var is mounted on its own partition enables the setting of more restrictive mount options. This helps protect system services such as daemons or other programs which use it. It is not uncommon for the /var directory to contain world-writable directories installed by other software packages.
BP28(R12) Ensure /var/log Located On Separate Partition System logs are stored in the /var/log directory. Ensure that it has its own partition or logical volume at installation time, or migrate it using LVM. Placing /var/log in its own partition enables better separation between log files and other files in /var/.
BP28(R12) Ensure /var/tmp Located On Separate Partition The /var/tmp directory is a world-writable directory used for temporary file storage. Ensure it has its own partition or logical volume at installation time, or migrate it using LVM. The /var/tmp partition is used as temporary storage by many programs. Placing /var/tmp in its own partition enables the setting of more restrictive mount options, which can help protect programs which use it.
BP28(R12) Add noauto Option to /boot The noauto mount option is used to prevent automatic mounting of th /boot partition. Add the noauto option to the fourth column of /etc/fstab for the line which controls mounting of /boot. The /boot partition contains the kernel and the bootloader. Access to the partition after the boot process finishes should not be needed. Files contained within this partition can be analysed and gained information can be used for exploit creation.
BP28(R12) Add noexec Option to /boot The noexec mount option can be used to prevent binaries from being executed out of /boot. Add the noexec option to the fourth column of /etc/fstab for the line which controls mounting of /boot. The /boot partition contains the kernel and the bootloader. No binaries should be executed from this partition after the booting process finishes.
BP28(R12) Add nosuid Option to /boot The nosuid mount option can be used to prevent execution of setuid programs in /boot. The SUID and SGID permissions should not be required on the boot partition. Add the nosuid option to the fourth column of /etc/fstab for the line which controls mounting of /boot. The presence of SUID and SGID executables should be tightly controlled. Users should not be able to execute SUID or SGID binaries from boot partitions.
BP28(R12) Add nodev Option to /home The nodev mount option can be used to prevent device files from being created in /home. Legitimate character and block devices should exist only in the /dev directory on the root partition or within chroot jails built for system services. Add the nodev option to the fourth column of /etc/fstab for the line which controls mounting of /home. The only legitimate location for device files is the /dev directory located on the root partition. The only exception to this is chroot jails.
BP28(R12) Add noexec Option to /home The noexec mount option can be used to prevent binaries from being executed out of /home. Add the noexec option to the fourth column of /etc/fstab for the line which controls mounting of /home. The /home directory contains data of individual users. Binaries in this directory should not be considered as trusted and users should not be able to execute them.
BP28(R12) Add nosuid Option to /home The nosuid mount option can be used to prevent execution of setuid programs in /home. The SUID and SGID permissions should not be required in these user data directories. Add the nosuid option to the fourth column of /etc/fstab for the line which controls mounting of /home. The presence of SUID and SGID executables should be tightly controlled. Users should not be able to execute SUID or SGID binaries from user home directory partitions.
BP28(R12) Add nodev Option to Non-Root Local Partitions The nodev mount option prevents files from being interpreted as character or block devices. Legitimate character and block devices should exist only in the /dev directory on the root partition or within chroot jails built for system services. Add the nodev option to the fourth column of /etc/fstab for the line which controls mounting of any non-root local partitions. The nodev mount option prevents files from being interpreted as character or block devices. The only legitimate location for device files is the /dev directory located on the root partition. The only exception to this is chroot jails, for which it is not advised to set nodev on these filesystems.
BP28(R12) Add nosuid Option to /opt The nosuid mount option can be used to prevent execution of setuid programs in /opt. The SUID and SGID permissions should not be required in this directory. Add the nosuid option to the fourth column of /etc/fstab for the line which controls mounting of /opt. The presence of SUID and SGID executables should be tightly controlled. The /opt directory contains additional software packages. Users should not be able to execute SUID or SGID binaries from this directory.
BP28(R12) Add nosuid Option to /srv The nosuid mount option can be used to prevent execution of setuid programs in /srv. The SUID and SGID permissions should not be required in this directory. Add the nosuid option to the fourth column of /etc/fstab for the line which controls mounting of /srv. The presence of SUID and SGID executables should be tightly controlled. The /srv directory contains files served by various network services such as FTP. Users should not be able to execute SUID or SGID binaries from this directory.
BP28(R12) Add nodev Option to /tmp The nodev mount option can be used to prevent device files from being created in /tmp. Legitimate character and block devices should not exist within temporary directories like /tmp. Add the nodev option to the fourth column of /etc/fstab for the line which controls mounting of /tmp. The only legitimate location for device files is the /dev directory located on the root partition. The only exception to this is chroot jails.
BP28(R12) Add noexec Option to /tmp The noexec mount option can be used to prevent binaries from being executed out of /tmp. Add the noexec option to the fourth column of /etc/fstab for the line which controls mounting of /tmp. Allowing users to execute binaries from world-writable directories such as /tmp should never be necessary in normal operation and can expose the system to potential compromise.
BP28(R12) Add nosuid Option to /tmp The nosuid mount option can be used to prevent execution of setuid programs in /tmp. The SUID and SGID permissions should not be required in these world-writable directories. Add the nosuid option to the fourth column of /etc/fstab for the line which controls mounting of /tmp. The presence of SUID and SGID executables should be tightly controlled. Users should not be able to execute SUID or SGID binaries from temporary storage partitions.
BP28(R12) Add noexec Option to /var/log The noexec mount option can be used to prevent binaries from being executed out of /var/log. Add the noexec option to the fourth column of /etc/fstab for the line which controls mounting of /var/log. Allowing users to execute binaries from directories containing log files such as /var/log should never be necessary in normal operation and can expose the system to potential compromise.
BP28(R12) Add nosuid Option to /var/log The nosuid mount option can be used to prevent execution of setuid programs in /var/log. The SUID and SGID permissions should not be required in directories containing log files. Add the nosuid option to the fourth column of /etc/fstab for the line which controls mounting of /var/log. The presence of SUID and SGID executables should be tightly controlled. Users should not be able to execute SUID or SGID binaries from partitions designated for log files.
BP28(R12) Add noexec Option to /var The noexec mount option can be used to prevent binaries from being executed out of /var. Add the noexec option to the fourth column of /etc/fstab for the line which controls mounting of /var. The /var directory contains variable system data such as logs, mails and caches. No binaries should be executed from this directory.
BP28(R12) Add nosuid Option to /var The nosuid mount option can be used to prevent execution of setuid programs in /var. The SUID and SGID permissions should not be required for this directory. Add the nosuid option to the fourth column of /etc/fstab for the line which controls mounting of /var. The presence of SUID and SGID executables should be tightly controlled.
BP28(R12) Add nodev Option to /var/tmp The nodev mount option can be used to prevent device files from being created in /var/tmp. Legitimate character and block devices should not exist within temporary directories like /var/tmp. Add the nodev option to the fourth column of /etc/fstab for the line which controls mounting of /var/tmp. The only legitimate location for device files is the /dev directory located on the root partition. The only exception to this is chroot jails.
BP28(R12) Add noexec Option to /var/tmp The noexec mount option can be used to prevent binaries from being executed out of /var/tmp. Add the noexec option to the fourth column of /etc/fstab for the line which controls mounting of /var/tmp. Allowing users to execute binaries from world-writable directories such as /var/tmp should never be necessary in normal operation and can expose the system to potential compromise.
BP28(R12) Add nosuid Option to /var/tmp The nosuid mount option can be used to prevent execution of setuid programs in /var/tmp. The SUID and SGID permissions should not be required in these world-writable directories. Add the nosuid option to the fourth column of /etc/fstab for the line which controls mounting of /var/tmp. The presence of SUID and SGID executables should be tightly controlled. Users should not be able to execute SUID or SGID binaries from temporary storage partitions.
BP28(R13) Verify that local System.map file (if exists) is readable only by root Files containing sensitive informations should be protected by restrictive permissions. Most of the time, there is no need that these files need to be read by any non-root user To properly set the permissions of /boot/System.map-*, run the command: 
$ sudo chmod 0600 /boot/System.map-*
 The System.map file contains information about kernel symbols and can give some hints to generate local exploitation.
BP28(R15) Ensure gpgcheck Enabled In Main yum Configuration The gpgcheck option controls whether RPM packages' signatures are always checked prior to installation. To configure yum to check package signatures before installing them, ensure the following line appears in /etc/yum.conf in the [main] section: 
gpgcheck=1
 Changes to any software components can have significant effects on the overall security of the operating system. This requirement ensures the software has not been tampered with and that it has been provided by a trusted vendor.
Accordingly, patches, service packs, device drivers, or operating system components must be signed with a certificate recognized and approved by the organization.
Verifying the authenticity of the software prior to installation validates the integrity of the patch or upgrade received from a vendor. This ensures the software has not been tampered with and that it has been provided by a trusted vendor. Self-signed certificates are disallowed by this requirement. Certificates used to verify the software must be from an approved Certificate Authority (CA).
BP28(R15) Ensure gpgcheck Enabled for Local Packages yum should be configured to verify the signature(s) of local packages prior to installation. To configure yum to verify signatures of local packages, set the localpkg_gpgcheck to 1 in /etc/yum.conf. Changes to any software components can have significant effects to the overall security of the operating system. This requirement ensures the software has not been tampered and has been provided by a trusted vendor.

Accordingly, patches, service packs, device drivers, or operating system components must be signed with a certificate recognized and approved by the organization.
BP28(R15) Ensure gpgcheck Enabled for All yum Package Repositories To ensure signature checking is not disabled for any repos, remove any lines from files in /etc/yum.repos.d of the form: 
gpgcheck=0
 Verifying the authenticity of the software prior to installation validates the integrity of the patch or upgrade received from a vendor. This ensures the software has not been tampered with and that it has been provided by a trusted vendor. Self-signed certificates are disallowed by this requirement. Certificates used to verify the software must be from an approved Certificate Authority (CA)."
BP28(R17) Set the Boot Loader Admin Username to a Non-Default Value The grub2 boot loader should have a superuser account and password protection enabled to protect boot-time settings.

To maximize the protection, select a password-protected superuser account with unique name, and modify the /etc/grub.d/01_users configuration file to reflect the account name change.

Do not to use common administrator account names like root, admin, or administrator for the grub2 superuser account.

Change the superuser to a different username (The default is 'root'). 
$ sed -i 's/\(set superuser=\).*/\1"<unique user ID>"/g' /etc/grub.d/01_users


Once the superuser account has been added, update the grub.cfg file by running: 
grub2-mkconfig -o /boot/grub2/grub.cfg
 Having a non-default grub superuser username makes password-guessing attacks less effective.
BP28(R17) Set Boot Loader Password in grub2 The grub2 boot loader should have a superuser account and password protection enabled to protect boot-time settings.

Since plaintext passwords are a security risk, generate a hash for the password by running the following command: 
$ grub2-setpassword
When prompted, enter the password that was selected.



Once the superuser password has been added, update the grub.cfg file by running: 
grub2-mkconfig -o /boot/grub2/grub.cfg
 Password protection on the boot loader configuration ensures users with physical access cannot trivially alter important bootloader settings. These include which kernel to use, and whether to enter single-user mode.
BP28(R17) Set the UEFI Boot Loader Admin Username to a Non-Default Value The grub2 boot loader should have a superuser account and password protection enabled to protect boot-time settings.

To maximize the protection, select a password-protected superuser account with unique name, and modify the /etc/grub.d/01_users configuration file to reflect the account name change.

It is highly suggested not to use common administrator account names like root, admin, or administrator for the grub2 superuser account.

Change the superuser to a different username (The default is 'root'). 
$ sed -i 's/\(set superuser=\).*/\1"<unique user ID>"/g' /etc/grub.d/01_users


Once the superuser account has been added, update the grub.cfg file by running: 
grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg
 Having a non-default grub superuser username makes password-guessing attacks less effective.
BP28(R17) Set the UEFI Boot Loader Password The grub2 boot loader should have a superuser account and password protection enabled to protect boot-time settings.

Since plaintext passwords are a security risk, generate a hash for the password by running the following command: 
$ grub2-setpassword
When prompted, enter the password that was selected.

Once the superuser password has been added, update the grub.cfg file by running: 
grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg
 Password protection on the boot loader configuration ensures users with physical access cannot trivially alter important bootloader settings. These include which kernel to use, and whether to enter single-user mode.
BP28(R18) Limit Password Reuse Do not allow users to reuse recent passwords. This can be accomplished by using the remember option for the pam_unix or pam_pwhistory PAM modules.

In the file /etc/pam.d/system-auth, append remember= to the line which refers to the pam_unix.so or pam_pwhistory.somodule, as shown below:
  • for the pam_unix.so case: 
    password sufficient pam_unix.so ...existing_options... remember=
  • for the pam_pwhistory.so case: 
    password requisite pam_pwhistory.so ...existing_options... remember=
The DoD STIG requirement is 5 passwords.		 Preventing re-use of previous passwords helps ensure that a compromised password is not re-used by a user.
BP28(R18) Set Deny For Failed Password Attempts To configure the system to lock out accounts after a number of incorrect login attempts using pam_faillock.so, modify the content of both /etc/pam.d/system-auth and /etc/pam.d/password-auth as follows:

  • add the following line immediately before the pam_unix.so statement in the AUTH section: 
    auth required pam_faillock.so preauth silent deny= unlock_time= fail_interval=
  • add the following line immediately after the pam_unix.so statement in the AUTH section: 
    auth [default=die] pam_faillock.so authfail deny= unlock_time= fail_interval=
  • add the following line immediately before the pam_unix.so statement in the ACCOUNT section: 
    account required pam_faillock.so
 Locking out user accounts after a number of incorrect attempts prevents direct password guessing attacks.
BP28(R18) Configure the root Account for Failed Password Attempts To configure the system to lock out the root account after a number of incorrect login attempts using pam_faillock.so, modify the content of both /etc/pam.d/system-auth and /etc/pam.d/password-auth as follows:

  • Modify the following line in the AUTH section to add even_deny_root: 
    auth required pam_faillock.so preauth silent even_deny_root deny= unlock_time= fail_interval=
  • Modify the following line in the AUTH section to add even_deny_root: 
    auth [default=die] pam_faillock.so authfail even_deny_root deny= unlock_time= fail_interval=
 By limiting the number of failed logon attempts, the risk of unauthorized system access via user password guessing, otherwise known as brute-forcing, is reduced. Limits are imposed by locking the account.
BP28(R18) Set Interval For Counting Failed Password Attempts Utilizing pam_faillock.so, the fail_interval directive configures the system to lock out an account after a number of incorrect login attempts within a specified time period. Modify the content of both /etc/pam.d/system-auth and /etc/pam.d/password-auth as follows:

  • Add the following line immediately before the pam_unix.so statement in the AUTH section: 
    auth required pam_faillock.so preauth silent deny= unlock_time= fail_interval=
  • Add the following line immediately after the pam_unix.so statement in the AUTH section: 
    auth [default=die] pam_faillock.so authfail deny= unlock_time= fail_interval=
  • Add the following line immediately before the pam_unix.so statement in the ACCOUNT section: 
    account required pam_faillock.so
 By limiting the number of failed logon attempts the risk of unauthorized system access via user password guessing, otherwise known as brute-forcing, is reduced. Limits are imposed by locking the account.
BP28(R18) Set Lockout Time for Failed Password Attempts To configure the system to lock out accounts after a number of incorrect login attempts and require an administrator to unlock the account using pam_faillock.so, modify the content of both /etc/pam.d/system-auth and /etc/pam.d/password-auth as follows:

  • add the following line immediately before the pam_unix.so statement in the AUTH section: 
    auth required pam_faillock.so preauth silent deny= unlock_time= fail_interval=
  • add the following line immediately after the pam_unix.so statement in the AUTH section: 
    auth [default=die] pam_faillock.so authfail deny= unlock_time= fail_interval=
  • add the following line immediately before the pam_unix.so statement in the ACCOUNT section: 
    account required pam_faillock.so
If unlock_time is set to 0, manual intervention by an administrator is required to unlock a user.		 Locking out user accounts after a number of incorrect attempts prevents direct password guessing attacks. Ensuring that an administrator is involved in unlocking locked accounts draws appropriate attention to such situations.
BP28(R18) Ensure PAM Enforces Password Requirements - Minimum Digit Characters The pam_pwquality module's dcredit parameter controls requirements for usage of digits in a password. When set to a negative number, any password will be required to contain that many digits. When set to a positive number, pam_pwquality will grant +1 additional length credit for each digit. Modify the dcredit setting in /etc/security/pwquality.conf to require the use of a digit in passwords. Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.

Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised. Requiring digits makes password guessing attacks more difficult by ensuring a larger search space.
BP28(R18) Ensure PAM Enforces Password Requirements - Minimum Lowercase Characters The pam_pwquality module's lcredit parameter controls requirements for usage of lowercase letters in a password. When set to a negative number, any password will be required to contain that many lowercase characters. When set to a positive number, pam_pwquality will grant +1 additional length credit for each lowercase character. Modify the lcredit setting in /etc/security/pwquality.conf to require the use of a lowercase character in passwords. Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.

Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possble combinations that need to be tested before the password is compromised. Requiring a minimum number of lowercase characters makes password guessing attacks more difficult by ensuring a larger search space.
BP28(R18) Ensure PAM Enforces Password Requirements - Minimum Length The pam_pwquality module's minlen parameter controls requirements for minimum characters required in a password. Add minlen= after pam_pwquality to set minimum password length requirements. The shorter the password, the lower the number of possible combinations that need to be tested before the password is compromised.
Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks. Password length is one factor of several that helps to determine strength and how long it takes to crack a password. Use of more characters in a password helps to exponentially increase the time and/or resources required to compromose the password.
BP28(R18) Ensure PAM Enforces Password Requirements - Minimum Special Characters The pam_pwquality module's ocredit= parameter controls requirements for usage of special (or "other") characters in a password. When set to a negative number, any password will be required to contain that many special characters. When set to a positive number, pam_pwquality will grant +1 additional length credit for each special character. Modify the ocredit setting in /etc/security/pwquality.conf to equal to require use of a special character in passwords. Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.

Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possble combinations that need to be tested before the password is compromised. Requiring a minimum number of special characters makes password guessing attacks more difficult by ensuring a larger search space.
BP28(R18) Ensure PAM Enforces Password Requirements - Minimum Uppercase Characters The pam_pwquality module's ucredit= parameter controls requirements for usage of uppercase letters in a password. When set to a negative number, any password will be required to contain that many uppercase characters. When set to a positive number, pam_pwquality will grant +1 additional length credit for each uppercase character. Modify the ucredit setting in /etc/security/pwquality.conf to require the use of an uppercase character in passwords. Use of a complex password helps to increase the time and resources reuiqred to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.

Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised.
BP28(R18) Set Password Maximum Age To specify password maximum age for new accounts, edit the file /etc/login.defs and add or correct the following line: 
PASS_MAX_DAYS
A value of 180 days is sufficient for many environments. The DoD requirement is 60. The profile requirement is .		 Any password, no matter how complex, can eventually be cracked. Therefore, passwords need to be changed periodically. If the operating system does not limit the lifetime of passwords and force users to change their passwords, there is the risk that the operating system passwords could be compromised.

Setting the password maximum age ensures users are required to periodically change their passwords. Requiring shorter password lifetimes increases the risk of users writing down the password in a convenient location subject to physical compromise.
BP28(R18) Set Password Minimum Length in login.defs To specify password length requirements for new accounts, edit the file /etc/login.defs and add or correct the following line: 
PASS_MIN_LEN


The DoD requirement is 15. The FISMA requirement is 12. The profile requirement is . If a program consults /etc/login.defs and also another PAM module (such as pam_pwquality) during a password change operation, then the most restrictive must be satisfied. See PAM section for more information about enforcing password quality requirements.		 Requiring a minimum password length makes password cracking attacks more difficult by ensuring a larger search space. However, any security benefit from an onerous requirement must be carefully weighed against usability problems, support costs, or counterproductive behavior that may result.
BP28(R19) Install sudo Package The sudo package can be installed with the following command: 
$ sudo yum install sudo
 sudo is a program designed to allow a system administrator to give limited root privileges to users and log root activity. The basic philosophy is to give as few privileges as possible but still allow system users to get their work done.
BP28(R19) Direct root Logins Not Allowed To further limit access to the root account, administrators can disable root logins at the console by editing the /etc/securetty file. This file lists all devices the root user is allowed to login to. If the file does not exist at all, the root user can login through any communication device on the system, whether via the console or via a raw network interface. This is dangerous as user can login to the system as root via Telnet, which sends the password in plain text over the network. By default, Oracle Linux 7's /etc/securetty file only allows the root user to login at the console physically attached to the system. To prevent root from logging in, remove the contents of this file. To prevent direct root logins, remove the contents of this file by typing the following command: 
$ sudo echo > /etc/securetty
Disabling direct root logins ensures proper accountability and multifactor authentication to privileged accounts. Users will first login, then escalate to privileged (root) access via su / sudo. This is required for FISMA Low and FISMA Moderate systems.
BP28(R19) Ensure auditd Collects Information on the Use of Privileged Commands - sudo At a minimum, the audit system should collect the execution of privileged commands for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add a line of the following form to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F path=/usr/bin/sudo -F auid>=1000 -F auid!=unset -F key=privileged
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add a line of the following form to /etc/audit/audit.rules: 
-a always,exit -F path=/usr/bin/sudo -F auid>=1000 -F auid!=unset -F key=privileged
 Misuse of privileged functions, either intentionally or unintentionally by authorized users, or by unauthorized external entities that have compromised system accounts, is a serious and ongoing concern and can have significant adverse impacts on organizations. Auditing the use of privileged functions is one way to detect such misuse and identify the risk from insider and advanced persistent threats.

Privileged programs are subject to escalation-of-privilege attacks, which attempt to subvert their normal role of providing some necessary but limited capability. As such, motivation exists to monitor these programs for unusual activity.
BP28(R19) Disable SSH Root Login The root user should never be allowed to login to a system directly over a network. To disable root login via SSH, add or correct the following line in /etc/ssh/sshd_config: 
PermitRootLogin no
 Even though the communications channel may be encrypted, an additional layer of security is gained by extending the policy of not logging directly on as root. In addition, logging in with a user-specific account provides individual accountability of actions performed on the system and also helps to minimize direct attack attempts on root's password.
BP28(R22) Configure Accepting Default Router in Router Advertisements on All IPv6 Interfaces To set the runtime status of the net.ipv6.conf.all.accept_ra_defrtr kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv6.conf.all.accept_ra_defrtr=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv6.conf.all.accept_ra_defrtr = 0
 An illicit router advertisement message could result in a man-in-the-middle attack.
BP28(R22) Configure Accepting Prefix Information in Router Advertisements on All IPv6 Interfaces To set the runtime status of the net.ipv6.conf.all.accept_ra_pinfo kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv6.conf.all.accept_ra_pinfo=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv6.conf.all.accept_ra_pinfo = 0
 An illicit router advertisement message could result in a man-in-the-middle attack.
BP28(R22) Configure Accepting Router Preference in Router Advertisements on All IPv6 Interfaces To set the runtime status of the net.ipv6.conf.all.accept_ra_rtr_pref kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv6.conf.all.accept_ra_rtr_pref=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv6.conf.all.accept_ra_rtr_pref = 0
 An illicit router advertisement message could result in a man-in-the-middle attack.
BP28(R22) Disable Accepting ICMP Redirects for All IPv6 Interfaces To set the runtime status of the net.ipv6.conf.all.accept_redirects kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv6.conf.all.accept_redirects=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv6.conf.all.accept_redirects = 0
 An illicit ICMP redirect message could result in a man-in-the-middle attack.
BP28(R22) Disable Kernel Parameter for Accepting Source-Routed Packets on all IPv6 Interfaces To set the runtime status of the net.ipv6.conf.all.accept_source_route kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv6.conf.all.accept_source_route=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv6.conf.all.accept_source_route = 0
 Source-routed packets allow the source of the packet to suggest routers forward the packet along a different path than configured on the router, which can be used to bypass network security measures. This requirement applies only to the forwarding of source-routerd traffic, such as when IPv6 forwarding is enabled and the system is functioning as a router.

Accepting source-routed packets in the IPv6 protocol has few legitimate uses. It should be disabled unless it is absolutely required.
BP28(R22) Configure Auto Configuration on All IPv6 Interfaces To set the runtime status of the net.ipv6.conf.all.autoconf kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv6.conf.all.autoconf=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv6.conf.all.autoconf = 0
 An illicit router advertisement message could result in a man-in-the-middle attack.
BP28(R22) Configure Maximum Number of Autoconfigured Addresses on All IPv6 Interfaces To set the runtime status of the net.ipv6.conf.all.max_addresses kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv6.conf.all.max_addresses=1
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv6.conf.all.max_addresses = 1
 The number of global unicast IPv6 addresses for each interface should be limited exactly to the number of statically configured addresses.
BP28(R22) Configure Denying Router Solicitations on All IPv6 Interfaces To set the runtime status of the net.ipv6.conf.all.router_solicitations kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv6.conf.all.router_solicitations=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv6.conf.all.router_solicitations = 0
 To prevent discovery of the system by other systems, router solicitation requests should be denied.
BP28(R22) Configure Accepting Default Router in Router Advertisements on All IPv6 Interfaces By Default To set the runtime status of the net.ipv6.conf.default.accept_ra_defrtr kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv6.conf.default.accept_ra_defrtr=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv6.conf.default.accept_ra_defrtr = 0
 An illicit router advertisement message could result in a man-in-the-middle attack.
BP28(R22) Configure Accepting Prefix Information in Router Advertisements on All IPv6 Interfaces By Default To set the runtime status of the net.ipv6.conf.default.accept_ra_pinfo kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv6.conf.default.accept_ra_pinfo=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv6.conf.default.accept_ra_pinfo = 0
 An illicit router advertisement message could result in a man-in-the-middle attack.
BP28(R22) Configure Accepting Router Preference in Router Advertisements on All IPv6 Interfaces By Default To set the runtime status of the net.ipv6.conf.default.accept_ra_rtr_pref kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv6.conf.default.accept_ra_rtr_pref=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv6.conf.default.accept_ra_rtr_pref = 0
 An illicit router advertisement message could result in a man-in-the-middle attack.
BP28(R22) Disable Kernel Parameter for Accepting ICMP Redirects by Default on IPv6 Interfaces To set the runtime status of the net.ipv6.conf.default.accept_redirects kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv6.conf.default.accept_redirects=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv6.conf.default.accept_redirects = 0
 An illicit ICMP redirect message could result in a man-in-the-middle attack.
BP28(R22) Disable Kernel Parameter for Accepting Source-Routed Packets on IPv6 Interfaces by Default To set the runtime status of the net.ipv6.conf.default.accept_source_route kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv6.conf.default.accept_source_route=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv6.conf.default.accept_source_route = 0
 Source-routed packets allow the source of the packet to suggest routers forward the packet along a different path than configured on the router, which can be used to bypass network security measures. This requirement applies only to the forwarding of source-routerd traffic, such as when IPv6 forwarding is enabled and the system is functioning as a router. Accepting source-routed packets in the IPv6 protocol has few legitimate uses. It should be disabled unless it is absolutely required.
BP28(R22) Configure Auto Configuration on All IPv6 Interfaces By Default To set the runtime status of the net.ipv6.conf.default.autoconf kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv6.conf.default.autoconf=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv6.conf.default.autoconf = 0
 An illicit router advertisement message could result in a man-in-the-middle attack.
BP28(R22) Configure Maximum Number of Autoconfigured Addresses on All IPv6 Interfaces By Default To set the runtime status of the net.ipv6.conf.default.max_addresses kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv6.conf.default.max_addresses=1
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv6.conf.default.max_addresses = 1
 The number of global unicast IPv6 addresses for each interface should be limited exactly to the number of statically configured addresses.
BP28(R22) Configure Denying Router Solicitations on All IPv6 Interfaces By Default To set the runtime status of the net.ipv6.conf.default.router_solicitations kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv6.conf.default.router_solicitations=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv6.conf.default.router_solicitations = 0
 To prevent discovery of the system by other systems, router solicitation requests should be denied.
BP28(R22) Disable Accepting ICMP Redirects for All IPv4 Interfaces To set the runtime status of the net.ipv4.conf.all.accept_redirects kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.conf.all.accept_redirects=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv4.conf.all.accept_redirects = 0
 ICMP redirect messages are used by routers to inform hosts that a more direct route exists for a particular destination. These messages modify the host's route table and are unauthenticated. An illicit ICMP redirect message could result in a man-in-the-middle attack.
This feature of the IPv4 protocol has few legitimate uses. It should be disabled unless absolutely required."
BP28(R22) Disable Kernel Parameter for Accepting Source-Routed Packets on all IPv4 Interfaces To set the runtime status of the net.ipv4.conf.all.accept_source_route kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.conf.all.accept_source_route=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv4.conf.all.accept_source_route = 0
 Source-routed packets allow the source of the packet to suggest routers forward the packet along a different path than configured on the router, which can be used to bypass network security measures. This requirement applies only to the forwarding of source-routerd traffic, such as when IPv4 forwarding is enabled and the system is functioning as a router.

Accepting source-routed packets in the IPv4 protocol has few legitimate uses. It should be disabled unless it is absolutely required.
BP28(R22) Enable Kernel Parameter to Log Martian Packets on all IPv4 Interfaces To set the runtime status of the net.ipv4.conf.all.log_martians kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.conf.all.log_martians=1
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv4.conf.all.log_martians = 1
 The presence of "martian" packets (which have impossible addresses) as well as spoofed packets, source-routed packets, and redirects could be a sign of nefarious network activity. Logging these packets enables this activity to be detected.
BP28(R22) Enable Kernel Parameter to Use Reverse Path Filtering on all IPv4 Interfaces To set the runtime status of the net.ipv4.conf.all.rp_filter kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.conf.all.rp_filter=1
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv4.conf.all.rp_filter = 1
 Enabling reverse path filtering drops packets with source addresses that should not have been able to be received on the interface they were received on. It should not be used on systems which are routers for complicated networks, but is helpful for end hosts and routers serving small networks.
BP28(R22) Disable Kernel Parameter for Accepting Secure ICMP Redirects on all IPv4 Interfaces To set the runtime status of the net.ipv4.conf.all.secure_redirects kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.conf.all.secure_redirects=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv4.conf.all.secure_redirects = 0
 Accepting "secure" ICMP redirects (from those gateways listed as default gateways) has few legitimate uses. It should be disabled unless it is absolutely required.
BP28(R22) Disable Kernel Parameter for Accepting ICMP Redirects by Default on IPv4 Interfaces To set the runtime status of the net.ipv4.conf.default.accept_redirects kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.conf.default.accept_redirects=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv4.conf.default.accept_redirects = 0
 ICMP redirect messages are used by routers to inform hosts that a more direct route exists for a particular destination. These messages modify the host's route table and are unauthenticated. An illicit ICMP redirect message could result in a man-in-the-middle attack.
This feature of the IPv4 protocol has few legitimate uses. It should be disabled unless absolutely required.
BP28(R22) Disable Kernel Parameter for Accepting Source-Routed Packets on IPv4 Interfaces by Default To set the runtime status of the net.ipv4.conf.default.accept_source_route kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.conf.default.accept_source_route=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv4.conf.default.accept_source_route = 0
 Source-routed packets allow the source of the packet to suggest routers forward the packet along a different path than configured on the router, which can be used to bypass network security measures.
Accepting source-routed packets in the IPv4 protocol has few legitimate uses. It should be disabled unless it is absolutely required, such as when IPv4 forwarding is enabled and the system is legitimately functioning as a router.
BP28(R22) Enable Kernel Parameter to Use Reverse Path Filtering on all IPv4 Interfaces by Default To set the runtime status of the net.ipv4.conf.default.rp_filter kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.conf.default.rp_filter=1
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv4.conf.default.rp_filter = 1
 Enabling reverse path filtering drops packets with source addresses that should not have been able to be received on the interface they were received on. It should not be used on systems which are routers for complicated networks, but is helpful for end hosts and routers serving small networks.
BP28(R22) Configure Kernel Parameter for Accepting Secure Redirects By Default To set the runtime status of the net.ipv4.conf.default.secure_redirects kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.conf.default.secure_redirects=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv4.conf.default.secure_redirects = 0
 Accepting "secure" ICMP redirects (from those gateways listed as default gateways) has few legitimate uses. It should be disabled unless it is absolutely required.
BP28(R22) Enable Kernel Parameter to Ignore Bogus ICMP Error Responses on IPv4 Interfaces To set the runtime status of the net.ipv4.icmp_ignore_bogus_error_responses kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.icmp_ignore_bogus_error_responses=1
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv4.icmp_ignore_bogus_error_responses = 1
 Ignoring bogus ICMP error responses reduces log size, although some activity would not be logged.
BP28(R22) Set Kernel Parameter to Increase Local Port Range To set the runtime status of the net.ipv4.ip_local_port_range kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.ip_local_port_range=32768 65535
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv4.ip_local_port_range = 32768 65535
 This setting defines the local port range that is used by TCP and UDP to choose the local port. The first number is the first, the second the last local port number.
BP28(R22) Enable Kernel Parameter to Use TCP RFC 1337 on IPv4 Interfaces To set the runtime status of the net.ipv4.tcp_rfc1337 kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.tcp_rfc1337=1
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv4.tcp_rfc1337 = 1
 Enable TCP behavior conformant with RFC 1337. When disabled, if a RST is received in TIME_WAIT state, we close the socket immediately without waiting for the end of the TIME_WAIT period.
BP28(R22) Enable Kernel Parameter to Use TCP Syncookies on IPv4 Interfaces To set the runtime status of the net.ipv4.tcp_syncookies kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.tcp_syncookies=1
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv4.tcp_syncookies = 1
 A TCP SYN flood attack can cause a denial of service by filling a system's TCP connection table with connections in the SYN_RCVD state. Syncookies can be used to track a connection when a subsequent ACK is received, verifying the initiator is attempting a valid connection and is not a flood source. This feature is activated when a flood condition is detected, and enables the system to continue servicing valid connection requests.
BP28(R22) Disable Kernel Parameter for Sending ICMP Redirects on all IPv4 Interfaces To set the runtime status of the net.ipv4.conf.all.send_redirects kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.conf.all.send_redirects=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv4.conf.all.send_redirects = 0
 ICMP redirect messages are used by routers to inform hosts that a more direct route exists for a particular destination. These messages contain information from the system's route table possibly revealing portions of the network topology.
The ability to send ICMP redirects is only appropriate for systems acting as routers.
BP28(R22) Disable Kernel Parameter for Sending ICMP Redirects on all IPv4 Interfaces by Default To set the runtime status of the net.ipv4.conf.default.send_redirects kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.conf.default.send_redirects=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv4.conf.default.send_redirects = 0
 ICMP redirect messages are used by routers to inform hosts that a more direct route exists for a particular destination. These messages contain information from the system's route table possibly revealing portions of the network topology.
The ability to send ICMP redirects is only appropriate for systems acting as routers.
BP28(R22) Disable Kernel Parameter for IP Forwarding on IPv4 Interfaces To set the runtime status of the net.ipv4.ip_forward kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.ip_forward=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv4.ip_forward = 0
 Routing protocol daemons are typically used on routers to exchange network topology information with other routers. If this capability is used when not required, system network information may be unnecessarily transmitted across the network.
BP28(R23) Enable Kernel Parameter to Enforce DAC on Hardlinks To set the runtime status of the fs.protected_hardlinks kernel parameter, run the following command: 
$ sudo sysctl -w fs.protected_hardlinks=1
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
fs.protected_hardlinks = 1
 By enabling this kernel parameter, users can no longer create soft or hard links to files which they do not own. Disallowing such hardlinks mitigate vulnerabilities based on insecure file system accessed by privileged programs, avoiding an exploitation vector exploiting unsafe use of open() or creat().
BP28(R23) Enable Kernel Parameter to Enforce DAC on Symlinks To set the runtime status of the fs.protected_symlinks kernel parameter, run the following command: 
$ sudo sysctl -w fs.protected_symlinks=1
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
fs.protected_symlinks = 1
 By enabling this kernel parameter, symbolic links are permitted to be followed only when outside a sticky world-writable directory, or when the UID of the link and follower match, or when the directory owner matches the symlink's owner. Disallowing such symlinks helps mitigate vulnerabilities based on insecure file system accessed by privileged programs, avoiding an exploitation vector exploiting unsafe use of open() or creat().
BP28(R23) Restrict Access to Kernel Message Buffer To set the runtime status of the kernel.dmesg_restrict kernel parameter, run the following command: 
$ sudo sysctl -w kernel.dmesg_restrict=1
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
kernel.dmesg_restrict = 1
 Unprivileged access to the kernel syslog can expose sensitive kernel address information.
BP28(R23) Limit CPU consumption of the Perf system To set the runtime status of the kernel.perf_cpu_time_max_percent kernel parameter, run the following command: 
$ sudo sysctl -w kernel.perf_cpu_time_max_percent=1
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
kernel.perf_cpu_time_max_percent = 1
 The kernel.perf_cpu_time_max_percent configures a treshold of maximum percentile of CPU that can be used by Perf system. Restricting usage of Perf system decreases risk of potential availability problems.
BP28(R23) Limit sampling frequency of the Perf system To set the runtime status of the kernel.perf_event_max_sample_rate kernel parameter, run the following command: 
$ sudo sysctl -w kernel.perf_event_max_sample_rate=1
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
kernel.perf_event_max_sample_rate = 1
 The kernel.perf_event_max_sample_rate parameter configures maximum frequency of collecting of samples for the Perf system. It is expressed in samples per second. Restricting usage of Perf system decreases risk of potential availability problems.
BP28(R23) Disallow kernel profiling by unprivileged users To set the runtime status of the kernel.perf_event_paranoid kernel parameter, run the following command: 
$ sudo sysctl -w kernel.perf_event_paranoid=2
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
kernel.perf_event_paranoid = 2
 Kernel profiling can reveal sensitive information about kernel behaviour.
BP28(R23) Configure maximum number of process identifiers To set the runtime status of the kernel.pid_max kernel parameter, run the following command: 
$ sudo sysctl -w kernel.pid_max=65536
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
kernel.pid_max = 65536
 The kernel.pid_max parameter configures upper limit on process identifiers (PID). If this number is not high enough, it might happen that forking of new processes is not possible, because all available PIDs are exhausted. Increasing this number enhances availability.
BP28(R23) Disallow magic SysRq key To set the runtime status of the kernel.sysrq kernel parameter, run the following command: 
$ sudo sysctl -w kernel.sysrq=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
kernel.sysrq = 0
 The Magic SysRq key allows sending certain commands directly to the running kernel. It can dump various system and process information, potentially revealing sensitive information. It can also reboot or shutdown the machine, disturbing its availability.
BP28(R23) Prevent applications from mapping low portion of virtual memory To set the runtime status of the vm.mmap_min_addr kernel parameter, run the following command: 
$ sudo sysctl -w vm.mmap_min_addr=65536
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
vm.mmap_min_addr = 65536
 The vm.mmap_min_addr parameter specifies the minimum virtual address that a process is allowed to mmap. Allowing a process to mmap low portion of virtual memory can have security implications such as such as heightened risk of kernel null pointer dereference defects.
BP28(R23) Disable Core Dumps for SUID programs To set the runtime status of the fs.suid_dumpable kernel parameter, run the following command: 
$ sudo sysctl -w fs.suid_dumpable=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
fs.suid_dumpable = 0
 The core dump of a setuid program is more likely to contain sensitive data, as the program itself runs with greater privileges than the user who initiated execution of the program. Disabling the ability for any setuid program to write a core file decreases the risk of unauthorized access of such data.
BP28(R23) Restrict Exposed Kernel Pointer Addresses Access To set the runtime status of the kernel.kptr_restrict kernel parameter, run the following command: 
$ sudo sysctl -w kernel.kptr_restrict=1
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
kernel.kptr_restrict = 1
 Exposing kernel pointers (through procfs or seq_printf()) exposes kernel writeable structures that can contain functions pointers. If a write vulnereability occurs in the kernel allowing a write access to any of this structure, the kernel can be compromise. This option disallow any program withtout the CAP_SYSLOG capability from getting the kernel pointers addresses, replacing them with 0.
BP28(R23) Enable Randomized Layout of Virtual Address Space To set the runtime status of the kernel.randomize_va_space kernel parameter, run the following command: 
$ sudo sysctl -w kernel.randomize_va_space=2
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
kernel.randomize_va_space = 2
 Address space layout randomization (ASLR) makes it more difficult for an attacker to predict the location of attack code they have introduced into a process's address space during an attempt at exploitation. Additionally, ASLR makes it more difficult for an attacker to know the location of existing code in order to re-purpose it using return oriented programming (ROP) techniques.
BP28(R24) Disable loading and unloading of kernel modules To set the runtime status of the kernel.modules_disabled kernel parameter, run the following command: 
$ sudo sysctl -w kernel.modules_disabled=1
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
kernel.modules_disabled = 1
 Malicious kernel modules can have a significant impact on system security and availability. Disabling loading of kernel modules prevents this threat. Note that once this option has been set, it cannot be reverted without doing a system reboot. Make sure that all needed kernel modules are loaded before setting this option.
BP28(R25) Restrict usage of ptrace to descendant processes To set the runtime status of the kernel.yama.ptrace_scope kernel parameter, run the following command: 
$ sudo sysctl -w kernel.yama.ptrace_scope=1
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
kernel.yama.ptrace_scope = 1
 Unrestricted usage of ptrace allows compromised binaries to run ptrace on another processes of the user. Like this, the attacker can steal sensitive information from the target processes (e.g. SSH sessions, web browser, ...) without any additional assistance from the user (i.e. without resorting to phishing).
BP28(R29) Set Interactive Session Timeout Setting the TMOUT option in /etc/profile ensures that all user sessions will terminate based on inactivity. The TMOUT setting in a file loaded by /etc/profile, e.g. /etc/profile.d/tmout.sh should read as follows: 
TMOUT=
 Terminating an idle session within a short time period reduces the window of opportunity for unauthorized personnel to take control of a management session enabled on the console or console port that has been left unattended.
BP28(R29) Set SSH Idle Timeout Interval SSH allows administrators to set an idle timeout interval. After this interval has passed, the idle user will be automatically logged out.

To set an idle timeout interval, edit the following line in /etc/ssh/sshd_config as follows: 
ClientAliveInterval


The timeout interval is given in seconds. For example, have a timeout of 10 minutes, set interval to 600.

If a shorter timeout has already been set for the login shell, that value will preempt any SSH setting made in /etc/ssh/sshd_config. Keep in mind that some processes may stop SSH from correctly detecting that the user is idle.		 Terminating an idle ssh session within a short time period reduces the window of opportunity for unauthorized personnel to take control of a management session enabled on the console or console port that has been let unattended.
BP28(R29) Set SSH Client Alive Count Max The SSH server sends at most ClientAliveCountMax messages during a SSH session and waits for a response from the SSH client. The option ClientAliveInterval configures timeout after each ClientAliveCountMax message. If the SSH server does not receive a response from the client, then the connection is considered idle and terminated. For SSH earlier than v8.2, a ClientAliveCountMax value of 0 causes an idle timeout precisely when the ClientAliveInterval is set. Starting with v8.2, a value of 0 disables the timeout functionality completely. If the option is set to a number greater than 0, then the idle session will be disconnected after ClientAliveInterval * ClientAliveCountMax seconds. This ensures a user login will be terminated as soon as the ClientAliveInterval is reached.
BP28(R32) Set Password Hashing Algorithm in /etc/login.defs In /etc/login.defs, add or correct the following line to ensure the system will use SHA-512 as the hashing algorithm: 
ENCRYPT_METHOD SHA512
 Passwords need to be protected at all times, and encryption is the standard method for protecting passwords. If passwords are not encrypted, they can be plainly read (i.e., clear text) and easily compromised. Passwords that are encrypted with a weak algorithm are no more protected than if they are kept in plain text.

Using a stronger hashing algorithm makes password cracking attacks more difficult.
BP28(R32) Set PAM's Password Hashing Algorithm The PAM system service can be configured to only store encrypted representations of passwords. In /etc/pam.d/system-auth, the password section of the file controls which PAM modules execute during a password change. Set the pam_unix.so module in the password section to include the argument sha512, as shown below: 
password    sufficient    pam_unix.so sha512 other arguments...

This will help ensure when local users change their passwords, hashes for the new passwords will be generated using the SHA-512 algorithm. This is the default.		 Passwords need to be protected at all times, and encryption is the standard method for protecting passwords. If passwords are not encrypted, they can be plainly read (i.e., clear text) and easily compromised. Passwords that are encrypted with a weak algorithm are no more protected than if they are kepy in plain text.

This setting ensures user and group account administration utilities are configured to store only encrypted representations of passwords. Additionally, the crypt_style configuration option ensures the use of a strong hashing algorithm that makes password cracking attacks more difficult.
BP28(R32) Set number of Password Hashing Rounds - password-auth Configure the number or rounds for the password hashing algorithm. This can be accomplished by using the rounds option for the pam_unix PAM module.

In file /etc/pam.d/password-auth append rounds= to the pam_unix.so file, as shown below: 
password sufficient pam_unix.so ...existing_options... rounds=
The system's default number of rounds is 5000.		 Using a higher number of rounds makes password cracking attacks more difficult.
BP28(R32) Set number of Password Hashing Rounds - system-auth Configure the number or rounds for the password hashing algorithm. This can be accomplished by using the rounds option for the pam_unix PAM module.

In file /etc/pam.d/system-auth append rounds= to the pam_unix.so file, as shown below: 
password sufficient pam_unix.so ...existing_options... rounds=
The system's default number of rounds is 5000.		 Using a higher number of rounds makes password cracking attacks more difficult.
BP28(R35) Ensure the Default Bash Umask is Set Correctly To ensure the default umask for users of the Bash shell is set properly, add or correct the umask setting in /etc/bashrc to read as follows: 
umask
The umask value influences the permissions assigned to files when they are created. A misconfigured umask value could result in files with excessive permissions that can be read or written to by unauthorized users.
BP28(R35) Ensure the Default Umask is Set Correctly in login.defs To ensure the default umask controlled by /etc/login.defs is set properly, add or correct the UMASK setting in /etc/login.defs to read as follows: 
UMASK
The umask value influences the permissions assigned to files when they are created. A misconfigured umask value could result in files with excessive permissions that can be read and written to by unauthorized users.
BP28(R35) Ensure the Default Umask is Set Correctly in /etc/profile To ensure the default umask controlled by /etc/profile is set properly, add or correct the umask setting in /etc/profile to read as follows: 
umask
The umask value influences the permissions assigned to files when they are created. A misconfigured umask value could result in files with excessive permissions that can be read or written to by unauthorized users.
BP28(R36) Ensure System Log Files Have Correct Permissions The file permissions for all log files written by rsyslog should be set to 600, or more restrictive. These log files are determined by the second part of each Rule line in /etc/rsyslog.conf and typically all appear in /var/log. For each log file LOGFILE referenced in /etc/rsyslog.conf, run the following command to inspect the file's permissions: 
$ ls -l LOGFILE
If the permissions are not 600 or more restrictive, run the following command to correct this: 
$ sudo chmod 0600 LOGFILE
"		 Log files can contain valuable information regarding system configuration. If the system log files are not protected unauthorized users could change the logged data, eliminating their forensic value.
BP28(R36) Verify User Who Owns gshadow File To properly set the owner of /etc/gshadow, run the command: 
$ sudo chown root /etc/gshadow
The /etc/gshadow file contains group password hashes. Protection of this file is critical for system security.
BP28(R36) Verify User Who Owns shadow File To properly set the owner of /etc/shadow, run the command: 
$ sudo chown root /etc/shadow
The /etc/shadow file contains the list of local system accounts and stores password hashes. Protection of this file is critical for system security. Failure to give ownership of this file to root provides the designated owner with access to sensitive information which could weaken the system security posture.
BP28(R36) Verify Permissions on group File To properly set the permissions of /etc/passwd, run the command: 
$ sudo chmod 0644 /etc/passwd
 The /etc/group file contains information regarding groups that are configured on the system. Protection of this file is important for system security.
BP28(R36) Verify Permissions on gshadow File To properly set the permissions of /etc/gshadow, run the command: 
$ sudo chmod 0000 /etc/gshadow
 The /etc/gshadow file contains group password hashes. Protection of this file is critical for system security.
BP28(R36) Verify Permissions on passwd File To properly set the permissions of /etc/passwd, run the command: 
$ sudo chmod 0644 /etc/passwd
 If the /etc/passwd file is writable by a group-owner or the world the risk of its compromise is increased. The file contains the list of accounts on the system and associated information, and protection of this file is critical for system security.
BP28(R36) Verify Permissions on shadow File To properly set the permissions of /etc/shadow, run the command: 
$ sudo chmod 0000 /etc/shadow
 The /etc/shadow file contains the list of local system accounts and stores password hashes. Protection of this file is critical for system security. Failure to give ownership of this file to root provides the designated owner with access to sensitive information which could weaken the system security posture.
BP28(R36) Verify Permissions on SSH Server Private *_key Key Files To properly set the permissions of /etc/ssh/*_key, run the command: 
$ sudo chmod 0600 /etc/ssh/*_key
 If an unauthorized user obtains the private SSH host key file, the host could be impersonated.
BP28(R37) Ensure All SGID Executables Are Authorized The SGID (set group id) bit should be set only on files that were installed via authorized means. A straightforward means of identifying unauthorized SGID files is determine if any were not installed as part of an RPM package, which is cryptographically verified. Investigate the origin of any unpackaged SGID files. This configuration check considers authorized SGID files which were installed via RPM. It is assumed that when an individual has sudo access to install an RPM and all packages are signed with an organizationally-recognized GPG key, the software should be considered an approved package on the system. Any SGID file not deployed through an RPM will be flagged for further review. Executable files with the SGID permission run with the privileges of the owner of the file. SGID files of uncertain provenance could allow for unprivileged users to elevate privileges. The presence of these files should be strictly controlled on the system.
BP28(R37) Ensure All SUID Executables Are Authorized The SUID (set user id) bit should be set only on files that were installed via authorized means. A straightforward means of identifying unauthorized SUID files is determine if any were not installed as part of an RPM package, which is cryptographically verified. Investigate the origin of any unpackaged SUID files. This configuration check considers authorized SUID files which were installed via RPM. It is assumed that when an individual has sudo access to install an RPM and all packages are signed with an organizationally-recognized GPG key, the software should be considered an approved package on the system. Any SUID file not deployed through an RPM will be flagged for further review. Executable files with the SUID permission run with the privileges of the owner of the file. SUID files of uncertain provenance could allow for unprivileged users to elevate privileges. The presence of these files should be strictly controlled on the system.
BP28(R38) Ensure All SGID Executables Are Authorized The SGID (set group id) bit should be set only on files that were installed via authorized means. A straightforward means of identifying unauthorized SGID files is determine if any were not installed as part of an RPM package, which is cryptographically verified. Investigate the origin of any unpackaged SGID files. This configuration check considers authorized SGID files which were installed via RPM. It is assumed that when an individual has sudo access to install an RPM and all packages are signed with an organizationally-recognized GPG key, the software should be considered an approved package on the system. Any SGID file not deployed through an RPM will be flagged for further review. Executable files with the SGID permission run with the privileges of the owner of the file. SGID files of uncertain provenance could allow for unprivileged users to elevate privileges. The presence of these files should be strictly controlled on the system.
BP28(R38) Ensure All SUID Executables Are Authorized The SUID (set user id) bit should be set only on files that were installed via authorized means. A straightforward means of identifying unauthorized SUID files is determine if any were not installed as part of an RPM package, which is cryptographically verified. Investigate the origin of any unpackaged SUID files. This configuration check considers authorized SUID files which were installed via RPM. It is assumed that when an individual has sudo access to install an RPM and all packages are signed with an organizationally-recognized GPG key, the software should be considered an approved package on the system. Any SUID file not deployed through an RPM will be flagged for further review. Executable files with the SUID permission run with the privileges of the owner of the file. SUID files of uncertain provenance could allow for unprivileged users to elevate privileges. The presence of these files should be strictly controlled on the system.
BP28(R39) Set Up a Private Namespace in PAM Configuration To setup a private namespace add the following line to /etc/pam.d/login: 
session    required     pam_namespace.so
 The pam_namespace PAM module sets up a private namespace for a session with polyinstantiated directories. A polyinstantiated directory provides a different instance of itself based on user name, or when using SELinux, user name, security context or both. The polyinstatied directories can be used to dedicate separate temporary directories to each account.
BP28(R39) Configure Polyinstantiation of /tmp Directories To configure polyinstantiated /tmp directories, first create the parent directories which will hold the polyinstantiation child directories. Use the following command: 
$ sudo mkdir --mode 000 /tmp/tmp-inst
Then, add the following entry to /etc/security/namespace.conf: 
/tmp     /tmp/tmp-inst/            level      root,adm
 Polyinstantiation of temporary directories is a proactive security measure which reduces chances of attacks that are made possible by /tmp directories being world-writable.
BP28(R39) Configure Polyinstantiation of /var/tmp Directories To configure polyinstantiated /tmp directories, first create the parent directories which will hold the polyinstantiation child directories. Use the following command: 
$ sudo mkdir --mode 000 /var/tmp/tmp-inst
Then, add the following entry to /etc/security/namespace.conf: 
/var/tmp /var/tmp/tmp-inst/    level      root,adm
 Polyinstantiation of temporary directories is a proactive security measure which reduces chances of attacks that are made possible by /var/tmp directories being world-writable.
BP28(R39) Disable the polyinstantiation_enabled SELinux Boolean By default, the SELinux boolean polyinstantiation_enabled is disabled. If this setting is enabled, it should be disabled. To disable the polyinstantiation_enabled SELinux boolean, run the following command: 
$ sudo setsebool -P polyinstantiation_enabled off
BP28(R40) Ensure All World-Writable Directories Are Owned by root user All directories in local partitions which are world-writable should be owned by root. If any world-writable directories are not owned by root, this should be investigated. Following this, the files should be deleted or assigned to root user. Allowing a user account to own a world-writable directory is undesirable because it allows the owner of that directory to remove or replace any files that may be placed in the directory by other users.
BP28(R40) Verify that All World-Writable Directories Have Sticky Bits Set When the so-called 'sticky bit' is set on a directory, only the owner of a given file may remove that file from the directory. Without the sticky bit, any user with write access to a directory may remove any file in the directory. Setting the sticky bit prevents users from removing each other's files. In cases where there is no reason for a directory to be world-writable, a better solution is to remove that permission rather than to set the sticky bit. However, if a directory is used by a particular application, consult that application's documentation instead of blindly changing modes.
To set the sticky bit on a world-writable directory DIR, run the following command: 
$ sudo chmod +t DIR
 Failing to set the sticky bit on public directories allows unauthorized users to delete files in the directory structure.

The only authorized public directories are those temporary directories supplied with the system, or those designed to be temporary file repositories. The setting is normally reserved for directories used by the system, by users for temporary file storage (such as /tmp), and for directories requiring global read/write access.
BP28(R40) Ensure No World-Writable Files Exist It is generally a good idea to remove global (other) write access to a file when it is discovered. However, check with documentation for specific applications before making changes. Also, monitor for recurring world-writable files, as these may be symptoms of a misconfigured application or user account. Finally, this applies to real files and not virtual files that are a part of pseudo file systems such as sysfs or procfs. Data in world-writable files can be modified by any user on the system. In almost all circumstances, files can be configured using a combination of user and group permissions to support whatever legitimate access is needed without the risk caused by world-writable files.
BP28(R43) Ensure /var/log/audit Located On Separate Partition Audit logs are stored in the /var/log/audit directory. Ensure that it has its own partition or logical volume at installation time, or migrate it later using LVM. Make absolutely certain that it is large enough to store all audit logs that will be created by the auditing daemon. Placing /var/log/audit in its own partition enables better separation between audit files and other files, and helps ensure that auditing cannot be halted due to the partition running out of space.
BP28(R43) Ensure Logrotate Runs Periodically The logrotate utility allows for the automatic rotation of log files. The frequency of rotation is specified in /etc/logrotate.conf, which triggers a cron task. To configure logrotate to run daily, add or correct the following line in /etc/logrotate.conf: 
# rotate log files frequency
daily
 Log files that are not properly rotated run the risk of growing so large that they fill up the /var/log partition. Valuable logging information could be lost if the /var/log partition becomes full.
BP28(R43) The Chrony package is installed System time should be synchronized between all systems in an environment. This is typically done by establishing an authoritative time server or set of servers and having all systems synchronize their clocks to them. The chrony package can be installed with the following command: 
$ sudo yum install chrony
 Time synchronization is important to support time sensitive security mechanisms like Kerberos and also ensures log files have consistent time records across the enterprise, which aids in forensic investigations.
BP28(R43) A remote time server for Chrony is configured Chrony is a daemon which implements the Network Time Protocol (NTP). It is designed to synchronize system clocks across a variety of systems and use a source that is highly accurate. More information on chrony can be found at http://chrony.tuxfamily.org/. Chrony can be configured to be a client and/or a server. Add or edit server or pool lines to /etc/chrony.conf as appropriate: 
server <remote-server>
Multiple servers may be configured.		 If chrony is in use on the system proper configuration is vital to ensuring time synchronization is working properly.
BP28(R46) Ensure Log Files Are Owned By Appropriate Group The group-owner of all log files written by rsyslog should be . These log files are determined by the second part of each Rule line in /etc/rsyslog.conf and typically all appear in /var/log. For each log file LOGFILE referenced in /etc/rsyslog.conf, run the following command to inspect the file's group owner: 
$ ls -l LOGFILE
If the owner is not , run the following command to correct this: 
$ sudo chgrp  LOGFILE
 The log files generated by rsyslog contain valuable information regarding system configuration, user authentication, and other such information. Log files should be protected from unauthorized access.
BP28(R46) Ensure Log Files Are Owned By Appropriate User The owner of all log files written by rsyslog should be . These log files are determined by the second part of each Rule line in /etc/rsyslog.conf and typically all appear in /var/log. For each log file LOGFILE referenced in /etc/rsyslog.conf, run the following command to inspect the file's owner: 
$ ls -l LOGFILE
If the owner is not , run the following command to correct this: 
$ sudo chown  LOGFILE
 The log files generated by rsyslog contain valuable information regarding system configuration, user authentication, and other such information. Log files should be protected from unauthorized access.
BP28(R46) Ensure syslog-ng is Installed syslog-ng can be installed in replacement of rsyslog. The syslog-ng-core package can be installed with the following command: 
$ sudo yum install syslog-ng-core
 The syslog-ng-core package provides the syslog-ng daemon, which provides system logging services.
BP28(R46) Enable syslog-ng Service The syslog-ng service (in replacement of rsyslog) provides syslog-style logging by default on Debian. The syslog-ng service can be enabled with the following command: 
$ sudo systemctl enable syslog-ng.service
 The syslog-ng service must be running in order to provide logging services, which are essential to system administration.
BP28(R47) Ensure /var/log Located On Separate Partition System logs are stored in the /var/log directory. Ensure that it has its own partition or logical volume at installation time, or migrate it using LVM. Placing /var/log in its own partition enables better separation between log files and other files in /var/.
BP28(R48) Disable Postfix Network Listening Edit the file /etc/postfix/main.cf to ensure that only the following inet_interfaces line appears: 
inet_interfaces =
This ensures postfix accepts mail messages (such as cron job reports) from the local system only, and not from the network, which protects it from network attack.
BP28(R49) Configure System to Forward All Mail For The Root Account Make sure that mails delivered to root user are forwarded to a monitored email address. Make sure that the address is a valid email address reachable from the system in question. Use the following command to configure the alias: 
$ sudo echo "root: " >> /etc/aliases
$ sudo newaliases
 A number of system services utilize email messages sent to the root user to notify system administrators of active or impending issues. These messages must be forwarded to at least one monitored email address.
BP28(R50) Ensure the audit Subsystem is Installed The audit package should be installed. The auditd service is an access monitoring and accounting daemon, watching system calls to audit any access, in comparison with potential local access control policy such as SELinux policy.
BP28(R50) Install the cron service The Cron service should be installed. The cron service allow periodic job execution, needed for almost all administrative tasks and services (software update, log rotating, etc.). Access to cron service should be restricted to administrative accounts only.
BP28(R51) Install AIDE The aide package can be installed with the following command: 
$ sudo yum install aide
 The AIDE package must be installed if it is to be available for integrity checking.
BP28(R51) Build and Test AIDE Database Run the following command to generate a new database: 
$ sudo /usr/sbin/aide --init
By default, the database will be written to the file /var/lib/aide/aide.db.new.gz. Storing the database, the configuration file /etc/aide.conf, and the binary /usr/sbin/aide (or hashes of these files), in a secure location (such as on read-only media) provides additional assurance about their integrity. The newly-generated database can be installed as follows: 
$ sudo cp /var/lib/aide/aide.db.new.gz /var/lib/aide/aide.db.gz
To initiate a manual check, run the following command: 
$ sudo /usr/sbin/aide --check
If this check produces any unexpected output, investigate.		 For AIDE to be effective, an initial database of "known-good" information about files must be captured and it should be able to be verified against the installed files.
BP28(R51) Configure Periodic Execution of AIDE At a minimum, AIDE should be configured to run a weekly scan. To implement a daily execution of AIDE at 4:05am using cron, add the following line to /etc/crontab: 
05 4 * * * root /usr/sbin/aide --check
To implement a weekly execution of AIDE at 4:05am using cron, add the following line to /etc/crontab: 
05 4 * * 0 root /usr/sbin/aide --check
AIDE can be executed periodically through other means; this is merely one example. The usage of cron's special time codes, such as @daily and @weekly is acceptable.		 By default, AIDE does not install itself for periodic execution. Periodically running AIDE is necessary to reveal unexpected changes in installed files.

Unauthorized changes to the baseline configuration could make the system vulnerable to various attacks or allow unauthorized access to the operating system. Changes to operating system configurations can have unintended side effects, some of which may be relevant to security.

Detecting such changes and providing an automated response can help avoid unintended, negative consequences that could ultimately affect the security state of the operating system. The operating system's Information Management Officer (IMO)/Information System Security Officer (ISSO) and System Administrators (SAs) must be notified via email and/or monitoring system trap when there is an unauthorized modification of a configuration item.
BP28(R51) Configure Notification of Post-AIDE Scan Details AIDE should notify appropriate personnel of the details of a scan after the scan has been run. If AIDE has already been configured for periodic execution in /etc/crontab, append the following line to the existing AIDE line: 
 | /bin/mail -s "$(hostname) - AIDE Integrity Check" root@localhost
Otherwise, add the following line to /etc/crontab: 
05 4 * * * root /usr/sbin/aide --check | /bin/mail -s "$(hostname) - AIDE Integrity Check" root@localhost
AIDE can be executed periodically through other means; this is merely one example.		 Unauthorized changes to the baseline configuration could make the system vulnerable to various attacks or allow unauthorized access to the operating system. Changes to operating system configurations can have unintended side effects, some of which may be relevant to security.

Detecting such changes and providing an automated response can help avoid unintended, negative consequences that could ultimately affect the security state of the operating system. The operating system's Information Management Officer (IMO)/Information System Security Officer (ISSO) and System Administrators (SAs) must be notified via email and/or monitoring system trap when there is an unauthorized modification of a configuration item.
BP28(R51) Configure AIDE to Verify Access Control Lists (ACLs) By default, the acl option is added to the FIPSR ruleset in AIDE. If using a custom ruleset or the acl option is missing, add acl to the appropriate ruleset. For example, add acl to the following line in /etc/aide.conf: 
FIPSR = p+i+n+u+g+s+m+c+acl+selinux+xattrs+sha256
AIDE rules can be configured in multiple ways; this is merely one example that is already configured by default. The remediation provided with this rule adds acl to all rule sets available in /etc/aide.conf 		ACLs can provide permissions beyond those permitted through the file mode and must be verified by the file integrity tools.
BP28(R51) Configure AIDE to Verify Extended Attributes By default, the xattrs option is added to the FIPSR ruleset in AIDE. If using a custom ruleset or the xattrs option is missing, add xattrs to the appropriate ruleset. For example, add xattrs to the following line in /etc/aide.conf: 
FIPSR = p+i+n+u+g+s+m+c+acl+selinux+xattrs+sha256
AIDE rules can be configured in multiple ways; this is merely one example that is already configured by default. The remediation provided with this rule adds xattrs to all rule sets available in /etc/aide.conf 		Extended attributes in file systems are used to contain arbitrary data and file metadata with security implications.
BP28(R57) Ensure a dedicated group owns sudo Restrict the execution of privilege escalated commands to a dedicated group of users. Ensure the group owner of /usr/bin/sudo is . Restricting the set of users able to execute commands as privileged user reduces the attack surface.
BP28(R58) Ensure sudo Runs In A Minimal Environment - sudo env_reset The sudo env_reset tag, when specified, will run the command in a minimal environment, containing the TERM, PATH, HOME, MAIL, SHELL, LOGNAME, USER and SUDO_* variables. This should be enabled by making sure that the env_reset tag exists in /etc/sudoers configuration file or any sudo configuration snippets in /etc/sudoers.d/. Forcing sudo to reset the environment ensures that environment variables are not passed on to the command accidentaly, preventing leak of potentially sensitive information.
BP28(R58) Ensure sudo Ignores Commands In Current Dir - sudo ignore_dot The sudo ignore_dot tag, when specified, will ignore the current directory in the PATH environment variable. This should be enabled by making sure that the ignore_dot tag exists in /etc/sudoers configuration file or any sudo configuration snippets in /etc/sudoers.d/. Ignoring the commands in the user's current directory prevents an attacker from executing commands downloaded locally.
BP28(R58) Ensure Privileged Escalated Commands Cannot Execute Other Commands - sudo NOEXEC The sudo NOEXEC tag, when specified, prevents user executed commands from executing other commands, like a shell for example. This should be enabled by making sure that the NOEXEC tag exists in /etc/sudoers configuration file or any sudo configuration snippets in /etc/sudoers.d/. Restricting the capability of sudo allowed commands to execute sub-commands prevents users from running programs with privileges they wouldn't have otherwise.
BP28(R58) Ensure sudo passwd_timeout is appropriate - sudo passwd_timeout The sudo passwd_timeout tag sets the amount of time sudo password prompt waits. The passwd_timeout should be configured by making sure that the passwd_timeout=sub_var_value("var_sudo_passwd_timeout") tag exists in /etc/sudoers configuration file or any sudo configuration snippets in /etc/sudoers.d/. Reducing the time sudo waits for a a password reduces the time the process is exposed.
BP28(R58) Ensure Only Users Logged In To Real tty Can Execute Sudo - sudo requiretty The sudo requiretty tag, when specified, will only execute sudo commands from users logged in to a real tty. This should be enabled by making sure that the requiretty tag exists in /etc/sudoers configuration file or any sudo configuration snippets in /etc/sudoers.d/. Restricting the use cases in which a user is allowed to execute sudo commands reduces the attack surface.
BP28(R58) Ensure sudo umask is appropriate - sudo umask The sudo umask tag, when specified, will be added the to the user's umask in the command environment. The umask should be configured by making sure that the umask=sub_var_value("var_sudo_umask") tag exists in /etc/sudoers configuration file or any sudo configuration snippets in /etc/sudoers.d/. The umask value influences the permissions assigned to files when they are created. A misconfigured umask value could result in files with excessive permissions that can be read or written to by unauthorized users.
BP28(R58) Ensure Only Users Logged In To Real tty Can Execute Sudo - sudo use_pty The sudo use_pty tag, when specified, will only execute sudo commands from users logged in to a real tty. This should be enabled by making sure that the use_pty tag exists in /etc/sudoers configuration file or any sudo configuration snippets in /etc/sudoers.d/. Requiring that sudo commands be run in a pseudo-terminal can prevent an attacker from retaining access to the user's terminal after the main program has finished executing.
BP28(R59) Ensure Users Re-Authenticate for Privilege Escalation - sudo !authenticate The sudo !authenticate option, when specified, allows a user to execute commands using sudo without having to authenticate. This should be disabled by making sure that the !authenticate option does not exist in /etc/sudoers configuration file or any sudo configuration snippets in /etc/sudoers.d/. Without re-authentication, users may access resources or perform tasks for which they do not have authorization.

When operating systems provide the capability to escalate a functional capability, it is critical that the user re-authenticate.
BP28(R59) Ensure Users Re-Authenticate for Privilege Escalation - sudo NOPASSWD The sudo NOPASSWD tag, when specified, allows a user to execute commands using sudo without having to authenticate. This should be disabled by making sure that the NOPASSWD tag does not exist in /etc/sudoers configuration file or any sudo configuration snippets in /etc/sudoers.d/. Without re-authentication, users may access resources or perform tasks for which they do not have authorization.

When operating systems provide the capability to escalate a functional capability, it is critical that the user re-authenticate.
BP28(R60) Don't target root user in the sudoers file The targeted users of a user specification should be, as much as possible, non privileged users (i.e.: non-root). User specifications have to explicitly list the runas spec (i.e. the list of target users that can be impersonated), and ALL or root should not be used. It is common that the command to be executed does not require superuser rights (editing a file whose the owner is not root, sending a signal to an unprivileged process,etc.). In order to limit any attempt of privilege escalation through a command, it is better to apply normal user rights.
BP28(R61) Don't define allowed commands in sudoers by means of exclusion Policies applied by sudo through the sudoers file should not involve negation. Each user specification in the sudoers file contains a comma-delimited list of command specifications. The definition can make use glob patterns, as well as of negations. Indirect definition of those commands by means of exclusion of a set of commands is trivial to bypass, so it is not allowed to use such constructs. Specifying access right using negation is inefficient and can be easily circumvented. For example, it is expected that a specification like 
# To avoid absolutely , this rule can be easily circumvented!
user ALL = ALL ,!/ bin/sh
prevents the execution of the shell but that’s not the case: just copy the binary /bin/sh to a different name to make it executable again through the rule keyword ALL.
BP28(R63) Explicit arguments in sudo specifications All commands in the sudoers file must strictly specify the arguments allowed to be used for a given user. If the command is supposed to be executed only without arguments, pass "" as an argument in the corresponding user specification. Any argument can modify quite significantly the behavior of a program, whether regarding the realized operation (read, write, delete, etc.) or accessed resources (path in a file system tree). To avoid any possibility of misuse of a command by a user, the ambiguities must be removed at the level of its specification. For example, on some systems, the kernel messages are only accessible by root. If a user nevertheless must have the privileges to read them, the argument of the dmesg command has to be restricted in order to prevent the user from flushing the buffer through the -c option: 
user ALL = dmesg ""
BP28(R66) Configure SELinux Policy The SELinux targeted policy is appropriate for general-purpose desktops and servers, as well as systems in many other roles. To configure the system to use this policy, add or correct the following line in /etc/selinux/config: 
SELINUXTYPE=
Other policies, such as mls, provide additional security labeling and greater confinement but are not compatible with many general-purpose use cases.		 Setting the SELinux policy to targeted or a more specialized policy ensures the system will confine processes that are likely to be targeted for exploitation, such as network or system services.

Note: During the development or debugging of SELinux modules, it is common to temporarily place non-production systems in permissive mode. In such temporary cases, SELinux policies should be developed, and once work is completed, the system should be reconfigured to .
BP28(R66) Ensure SELinux State is Enforcing The SELinux state should be set to at system boot time. In the file /etc/selinux/config, add or correct the following line to configure the system to boot into enforcing mode: 
SELINUX=
 Setting the SELinux state to enforcing ensures SELinux is able to confine potentially compromised processes to the security policy, which is designed to prevent them from causing damage to the system or further elevating their privileges.
BP28(R67) Disable the secure_mode_insmod SELinux Boolean By default, the SELinux boolean secure_mode_insmod is disabled. If this setting is enabled, it should be disabled. To disable the secure_mode_insmod SELinux boolean, run the following command: 
$ sudo setsebool -P secure_mode_insmod off
BP28(R67) Disable the selinuxuser_execheap SELinux Boolean By default, the SELinux boolean selinuxuser_execheap is disabled. When enabled this boolean is enabled it allows selinuxusers to execute code from the heap. If this setting is enabled, it should be disabled. To disable the selinuxuser_execheap SELinux boolean, run the following command: 
$ sudo setsebool -P selinuxuser_execheap off
 Disabling code execution from the heap blocks buffer overflow attacks.
BP28(R67) disable the selinuxuser_execstack SELinux Boolean By default, the SELinux boolean selinuxuser_execstack is enabled. This setting should be disabled as unconfined executables should not be able to make their stack executable. To disable the selinuxuser_execstack SELinux boolean, run the following command: 
$ sudo setsebool -P selinuxuser_execstack off
 Disabling code execution from the stack blocks buffer overflow attacks.
BP28(R67) Disable the ssh_sysadm_login SELinux Boolean By default, the SELinux boolean ssh_sysadm_login is disabled. If this setting is enabled, it should be disabled. To disable the ssh_sysadm_login SELinux boolean, run the following command: 
$ sudo setsebool -P ssh_sysadm_login off
 Preventing non-privileged users from executing privileged functions mitigates the risk that unauthorized individuals or processes may gain unnecessary access to information or privileges. Privileged functions include, for example, establishing accounts, performing system integrity checks, or administering cryptographic key management activities. Non-privileged users are individuals who do not possess appropriate authorizations. Circumventing intrusion detection and prevention mechanisms or malicious code protection mechanisms are examples of privileged functions that require protection from non-privileged users.
BP28(R68) Uninstall setroubleshoot-plugins Package The SETroubleshoot plugins are used to analyze SELinux AVC data. The service provides information around configuration errors, unauthorized intrusions, and other potential errors. The setroubleshoot-plugins package can be removed with the following command: 
$ sudo yum erase setroubleshoot-plugins
 The SETroubleshoot service is an unnecessary daemon to have running on a server.
BP28(R68) Uninstall setroubleshoot Package The SETroubleshoot service notifies desktop users of SELinux denials. The service provides information around configuration errors, unauthorized intrusions, and other potential errors. The setroubleshoot package can be removed with the following command: 
$ sudo yum erase setroubleshoot
 The SETroubleshoot service is an unnecessary daemon to have running on a server, especially if X Windows is removed or disabled.
BP28(R68) Uninstall setroubleshoot-server Package The SETroubleshoot service notifies desktop users of SELinux denials. The service provides information around configuration errors, unauthorized intrusions, and other potential errors. The setroubleshoot-server package can be removed with the following command: 
$ sudo yum erase setroubleshoot-server
 The SETroubleshoot service is an unnecessary daemon to have running on a server.
NT007(R1) Allow Only SSH Protocol 2 Only SSH protocol version 2 connections should be permitted. The default setting in /etc/ssh/sshd_config is correct, and can be verified by ensuring that the following line appears: 
Protocol 2
 SSH protocol version 1 is an insecure implementation of the SSH protocol and has many well-known vulnerability exploits. Exploits of the SSH daemon could provide immediate root access to the system.
NT007(R02) Uninstall the ssl compliant telnet server The telnet daemon, even with ssl support, should be uninstalled. telnet, even with ssl support, should not be installed. When remote shell is required, up-to-date ssh daemon can be used.
NT007(R03) Uninstall the telnet server The telnet daemon should be uninstalled. telnet allows clear text communications, and does not protect any data transmission between client and server. Any confidential data can be listened and no integrity checking is made.'
NT007(R03) Uninstall the inet-based telnet server The inet-based telnet daemon should be uninstalled. telnet allows clear text communications, and does not protect any data transmission between client and server. Any confidential data can be listened and no integrity checking is made.
NT007(R17) Disable SSH Access via Empty Passwords To explicitly disallow SSH login from accounts with empty passwords, add or correct the following line in /etc/ssh/sshd_config: 
PermitEmptyPasswords no

Any accounts with empty passwords should be disabled immediately, and PAM configuration should prevent users from being able to assign themselves empty passwords.		 Configuring this setting for the SSH daemon provides additional assurance that remote login via SSH will require a password, even in the event of misconfiguration elsewhere.
NT007(R21) Disable SSH Root Login The root user should never be allowed to login to a system directly over a network. To disable root login via SSH, add or correct the following line in /etc/ssh/sshd_config: 
PermitRootLogin no
 Even though the communications channel may be encrypted, an additional layer of security is gained by extending the policy of not logging directly on as root. In addition, logging in with a user-specific account provides individual accountability of actions performed on the system and also helps to minimize direct attack attempts on root's password.
NT012(R03) Install the ntp service The ntpd service should be installed. Time synchronization (using NTP) is required by almost all network and administrative tasks (syslog, cryptographic based services (authentication, etc.), etc.). Ntpd is regulary maintained and updated, supporting security features such as RFC 5906.
NT012(R03) Enable the NTP Daemon The ntpd service can be enabled with the following command: 
$ sudo systemctl enable ntpd.service
 Enabling the ntpd service ensures that the ntpd service will be running and that the system will synchronize its time to any servers specified. This is important whether the system is configured to be a client (and synchronize only its own clock) or it is also acting as an NTP server to other systems. Synchronizing time is essential for authentication services such as Kerberos, but it is also important for maintaining accurate logs and auditing possible security breaches.

The NTP daemon offers all of the functionality of ntpdate, which is now deprecated.
NT12(R5) Ensure Logs Sent To Remote Host To configure rsyslog to send logs to a remote log server, open /etc/rsyslog.conf and read and understand the last section of the file, which describes the multiple directives necessary to activate remote logging. Along with these other directives, the system can be configured to forward its logs to a particular log server by adding or correcting one of the following lines, substituting appropriately. The choice of protocol depends on the environment of the system; although TCP and RELP provide more reliable message delivery, they may not be supported in all environments.
To use UDP for log message delivery: 
*.* @

To use TCP for log message delivery: 
*.* @@

To use RELP for log message delivery: 
*.* :omrelp:

There must be a resolvable DNS CNAME or Alias record set to "" for logs to be sent correctly to the centralized logging utility.		 A log server (loghost) receives syslog messages from one or more systems. This data can be used as an additional log source in the event a system is compromised and its local logs are suspect. Forwarding log messages to a remote loghost also provides system administrators with a centralized place to view the status of multiple hosts within the enterprise.
NT12(R18) Ensure Logrotate Runs Periodically The logrotate utility allows for the automatic rotation of log files. The frequency of rotation is specified in /etc/logrotate.conf, which triggers a cron task. To configure logrotate to run daily, add or correct the following line in /etc/logrotate.conf: 
# rotate log files frequency
daily
 Log files that are not properly rotated run the risk of growing so large that they fill up the /var/log partition. Valuable logging information could be lost if the /var/log partition becomes full.
NT28(R43) Ensure Logs Sent To Remote Host To configure rsyslog to send logs to a remote log server, open /etc/rsyslog.conf and read and understand the last section of the file, which describes the multiple directives necessary to activate remote logging. Along with these other directives, the system can be configured to forward its logs to a particular log server by adding or correcting one of the following lines, substituting appropriately. The choice of protocol depends on the environment of the system; although TCP and RELP provide more reliable message delivery, they may not be supported in all environments.
To use UDP for log message delivery: 
*.* @

To use TCP for log message delivery: 
*.* @@

To use RELP for log message delivery: 
*.* :omrelp:

There must be a resolvable DNS CNAME or Alias record set to "" for logs to be sent correctly to the centralized logging utility.		 A log server (loghost) receives syslog messages from one or more systems. This data can be used as an additional log source in the event a system is compromised and its local logs are suspect. Forwarding log messages to a remote loghost also provides system administrators with a centralized place to view the status of multiple hosts within the enterprise.
NT28(R46) Ensure rsyslog is Installed Rsyslog is installed by default. The rsyslog package can be installed with the following command: 
 $ sudo yum install rsyslog
 The rsyslog package provides the rsyslog daemon, which provides system logging services.
NT28(R46) Enable rsyslog Service The rsyslog service provides syslog-style logging by default on Oracle Linux 7. The rsyslog service can be enabled with the following command: 
$ sudo systemctl enable rsyslog.service
 The rsyslog service must be running in order to provide logging services, which are essential to system administration.