Configure OL 8 to display the Standard Mandatory DOD Notice and Consent Banner before granting access to the system via the SSH.

Edit the "/etc/ssh/sshd_config" file to uncomment the banner keyword and configure it to point to a file that will contain the logon banner (this file may be named differently or be in a different location if using a version of SSH that is provided by a third-party vendor). An example configuration line is:

banner /etc/issue

Either create the file containing the banner or replace the text in the file with the Standard Mandatory DOD Notice and Consent Banner. The DOD-required text is:

"You are accessing a U.S. Government (USG) Information System (IS) that is provided for USG-authorized use only. By using this IS (which includes any device attached to this IS), you consent to the following conditions:

-The USG routinely intercepts and monitors communications on this IS for purposes including, but not limited to, penetration testing, COMSEC monitoring, network operations and defense, personnel misconduct (PM), law enforcement (LE), and counterintelligence (CI) investigations.

-At any time, the USG may inspect and seize data stored on this IS.

-Communications using, or data stored on, this IS are not private, are subject to routine monitoring, interception, and search, and may be disclosed or used for any USG-authorized purpose.

-This IS includes security measures (e.g., authentication and access controls) to protect USG interests--not for your personal benefit or privacy.

-Notwithstanding the above, using this IS does not constitute consent to PM, LE or CI investigative searching or monitoring of the content of privileged communications, or work product, related to personal representation or services by attorneys, psychotherapists, or clergy, and their assistants. Such communications and work product are private and confidential. See User Agreement for details."

The SSH service must be restarted for changes to take effect.

Vulnerability Discussion

Check

For systems that use BIOS, this is not applicable.

Determine if an encrypted password is set for the grub superusers account. On systems that use UEFI, use the following command:

$ sudo grep -iw grub2_password /boot/efi/EFI/redhat/user.cfg

GRUB2_PASSWORD=grub.pbkdf2.sha512.[password_hash]

If the grub superusers account password does not begin with "grub.pbkdf2.sha512", this is a finding.

Fix

Configure the system to require an encrypted grub bootloader password for the grub superusers account with the grub2-setpassword command, which creates/overwrites the "/boot/efi/EFI/redhat/user.cfg" file.

Generate an encrypted grub2 password for the grub superusers account with the following command:

$ sudo grub2-setpassword
Enter password:
Confirm password:

OL 8 operating systems booted with United Extensible Firmware Interface (UEFI) must have a unique name for the grub superusers account when booting into single-user mode and maintenance.

Vulnerability Discussion

If the system does not require valid authentication before it boots into single-user or maintenance mode, anyone who invokes single-user or maintenance mode is granted privileged access to all files on the system. GRUB 2 is the default boot loader for OL 8 and is designed to require a password to boot into single-user mode or modify the boot menu.
The GRUB 2 superuser account is an account of last resort. Establishing a unique username for this account hardens the boot loader against brute force attacks. Due to the nature of the superuser account database being distinct from the OS account database, this allows the use of a username that is not among those within the OS account database. Examples of non-unique superusers names are (root, superuser, unlock, etc.)

Check

For systems that use BIOS, this is Not Applicable.

Verify that a unique name is set as the "superusers" account:

$ sudo grep -iw "superusers" /boot/efi/EFI/redhat/grub.cfg
set superusers="[someuniqueUserNamehere]"
export superusers

If "superusers" is identical to any OS account name or is missing a name, this is a finding.

Fix

Configure the system to replace "root" with a unique name for the grub superusers account.

Edit the /etc/grub.d/01_users file and add or modify the following lines:

set superusers="[someuniqueUserNamehere]"
export superusers
password_pbkdf2 [someuniqueUserNamehere] ${GRUB2_PASSWORD}

Generate a new grub.cfg file with the following command:

$ sudo grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg

OL 8 operating systems booted with a BIOS must have a unique name for the grub superusers account when booting into single-user and maintenance modes.

Vulnerability Discussion

Check

For systems that use UEFI, this is Not Applicable.

Verify that a unique name is set as the "superusers" account:

$ sudo grep -iw "superusers" /boot/grub2/grub.cfg
set superusers="[someuniqueUserNamehere]"
export superusers

If "superusers" is identical to any OS account name or is missing a name, this is a finding.

Fix

OL 8 operating systems booted with a BIOS must require authentication upon booting into single-user and maintenance modes.

Vulnerability Discussion

Check

For systems that use UEFI, this is not applicable.

Determine if an encrypted password is set for the grub superusers account. On systems that use a BIOS, use the following command:

$ sudo grep -iw grub2_password /boot/grub2/user.cfg

GRUB2_PASSWORD=grub.pbkdf2.sha512.[password_hash]

If the grub superusers account password does not begin with "grub.pbkdf2.sha512", this is a finding.

Fix

Configure the system to require a grub bootloader password for the grub superusers account with the grub2-setpassword command, which creates/overwrites the "/boot/grub2/user.cfg" file.

Generate an encrypted grub2 password for the grub superusers account with the following command:

$ sudo grub2-setpassword
Enter password:
Confirm password:

OL 8 operating systems must require authentication upon booting into rescue mode.

A sticky bit must be set on all OL 8 public directories to prevent unauthorized and unintended information transferred via shared system resources.

Vulnerability Discussion

Check

Verify that all world-writable directories have the sticky bit set.

Verify that all world-writable directories have the sticky bit set by running the following command:

$ sudo find / -type d $ -perm -0002 -a ! -perm -1000 $ -print 2>/dev/null

If any of the returned directories are world-writable and do not have the sticky bit set, this is a finding.

Fix

Configure all world-writable directories to have the sticky bit set to prevent unauthorized and unintended information transferred via shared system resources.

Set the sticky bit on all world-writable directories using the command, replace "[World-Writable Directory]" with any directory path missing the sticky bit:

$ sudo chmod 1777 [World-Writable Directory]

OL 8 must be configured so that all network connections associated with SSH traffic terminate after becoming unresponsive.

Vulnerability Discussion

Terminating an unresponsive 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 left unattended. In addition, quickly terminating an idle SSH session will also free up resources committed by the managed network element.

Terminating network connections associated with communications sessions includes, for example, de-allocating associated TCP/IP address/port pairs at the operating system level and de-allocating networking assignments at the application level if multiple application sessions are using a single operating system-level network connection. This does not mean that the operating system terminates all sessions or network access; it only ends the unresponsive session and releases the resources associated with that session.

OL 8 uses "/etc/ssh/sshd_config" for configurations of OpenSSH. Within the "sshd_config", the product of the values of "ClientAliveInterval" and "ClientAliveCountMax" is used to establish the inactivity threshold. The "ClientAliveInterval" is a timeout interval in seconds after which if no data has been received from the client, sshd will send a message through the encrypted channel to request a response from the client. The "ClientAliveCountMax" is the number of client alive messages that may be sent without sshd receiving any messages back from the client. If this threshold is met, sshd will disconnect the client. For more information on these settings and others, refer to the sshd_config man pages.

Satisfies: SRG-OS-000126-GPOS-00066, SRG-OS-000163-GPOS-00072, SRG-OS-000279-GPOS-00109

Check

Verify the SSH server automatically terminates a user session after the SSH client has become unresponsive.

Check that the "ClientAliveCountMax" is set to "1" by running the following command:

$ sudo /usr/sbin/sshd -dd 2>&1 | awk '/filename/ {print $4}' | tr -d '\r' | tr '\n' ' ' | xargs sudo grep -iH '^\s*clientalivecountmax'

ClientAliveCountMax 1

If "ClientAliveCountMax" does not exist, does not have a product value of "1" in "/etc/ssh/sshd_config", or is commented out, this is a finding.

If conflicting results are returned, this is a finding.

Fix

Note: This setting must be applied in conjunction with OL08-00-010201 to function correctly.

Configure the SSH server to terminate a user session automatically after the SSH client has become unresponsive.

Modify or append the following line in the "/etc/ssh/sshd_config" file:

ClientAliveCountMax 1

For the changes to take effect, the SSH daemon must be restarted.

$ sudo systemctl restart sshd.service

OL 8 must be configured so that all network connections associated with SSH traffic are terminated after 10 minutes of becoming unresponsive.

Vulnerability Discussion

Check

Verify the SSH server automatically terminates a user session after the SSH client has been unresponsive for 10 minutes.

Check that the "ClientAliveInterval" variable is set to a value of "600" or less by running the following command:

$ sudo /usr/sbin/sshd -dd 2>&1 | awk '/filename/ {print $4}' | tr -d '\r' | tr '\n' ' ' | xargs sudo grep -iH '^\s*clientaliveinterval'

ClientAliveInterval 600

If "ClientAliveInterval" does not exist, does not have a product value of "600" or less in "/etc/ssh/sshd_config", or is commented out, this is a finding.

If conflicting results are returned, this is a finding.

Fix

Note: This setting must be applied in conjunction with OL08-00-010200 to function correctly.

Configure the SSH server to terminate a user session automatically after the SSH client has been unresponsive for 10 minutes.

Modify or append the following lines in the "/etc/ssh/sshd_config" file to have a product value of "600" or less:

ClientAliveInterval 600

The SSH daemon must be restarted for changes to take effect.

$ sudo systemctl restart sshd.service

The OL 8 "/var/log/messages" file must have mode 0640 or less permissive.

OL 8 library directories must have mode 755 or less permissive.

OL 8 library files must be group-owned by root.

Vulnerability Discussion

Check

Verify the system-wide shared library files are group-owned by "root" with the following command:

$ sudo find -L /lib /lib64 /usr/lib /usr/lib64 ! -group root -exec ls -l {} \;

If any system-wide shared library file is returned, this is a finding.

Fix

OL 8 library directories must be group-owned by root or a system account.

Vulnerability Discussion

Check

Verify the system-wide shared library directories are group-owned by "root" with the following command:

$ sudo find /lib /lib64 /usr/lib /usr/lib64 ! -group root -type d -exec stat -c "%n %G" '{}' \;

If any system wide shared library directory is returned and is not group-owned by a required system account, this is a finding.

Fix

Configure the system-wide shared library directories (/lib, /lib64, /usr/lib and /usr/lib64) to be protected from unauthorized access.

Run the following command, replacing "[DIRECTORY]" with any library directory not group-owned by "root".

$ sudo chgrp root [DIRECTORY]

OL 8 file systems must not execute binary files that are imported via Network File System (NFS).

Local OL 8 initialization files must not execute world-writable programs.

Vulnerability Discussion

If user start-up files execute world-writable programs, especially in unprotected directories, they could be maliciously modified to destroy user files or otherwise compromise the system at the user level. If the system is compromised at the user level, it is easier to elevate privileges to eventually compromise the system at the root and network level.

Check

Verify that local initialization files do not execute world-writable programs.

Check the system for world-writable files.

The following command will discover and print world-writable files. Run it once for each local partition [PART]:

$ sudo find [PART] -xdev -type f -perm -0002 -print

For all files listed, check for their presence in the local initialization files with the following commands:

Note: The example will be for a system that is configured to create users' home directories in the "/home" directory.

$ sudo grep /home/*/.*

If any local initialization files are found to reference world-writable files, this is a finding.

Fix

Set the mode on files being executed by the local initialization files with the following command:

$ sudo chmod 0755

OL 8 must disable kernel dumps unless needed.

Check

Note: This requirement assumes the use of the OL 8 default graphical user interface, Gnome Shell. If the system does not have any graphical user interface installed, this requirement is Not Applicable.

Verify the operating system prevents a user from overriding settings for graphical user interfaces.

Determine which profile the system database is using with the following command:

$ sudo grep system-db /etc/dconf/profile/user

system-db:local

Check that graphical settings are locked from non-privileged user modification with the following command.

Note: The example below is using the database "local" for the system, so the path is "/etc/dconf/db/local.d". This path must be modified if a database other than "local" is being used.

$ sudo grep -i idle /etc/dconf/db/local.d/locks/*

/org/gnome/desktop/screensaver/idle-delay

If the command does not return at least the example result, this is a finding.

Fix

OL 8 must prevent a user from overriding the session lock-enabled setting for the graphical user interface.

Vulnerability Discussion

Check

Note: This requirement assumes the use of the OL 8 default graphical user interface, Gnome Shell. If the system does not have any graphical user interface installed, this requirement is Not Applicable.

Verify the operating system prevents a user from overriding settings for graphical user interfaces.

Determine which profile the system database is using with the following command:

$ sudo grep system-db /etc/dconf/profile/user

system-db:local

Check that graphical settings are locked from non-privileged user modification with the following command.

Note: The example below is using the database "local" for the system, so the path is "/etc/dconf/db/local.d". This path must be modified if a database other than "local" is being used.

$ sudo grep -i lock-enabled /etc/dconf/db/local.d/locks/*

/org/gnome/desktop/screensaver/lock-enabled

If the command does not return at least the example result, this is a finding.

Configure non-compliant accounts to enforce a 24 hours/1 day minimum password lifetime:

$ sudo chage -m 1 [user]

OL 8 passwords for new users or password changes must have a 24 hours/1 day minimum password lifetime restriction in "/etc/login.defs".

Vulnerability Discussion

Check

Verify the operating system enforces 24 hours/1 day as the minimum password lifetime for new user accounts.

Check for the value of "PASS_MIN_DAYS" in "/etc/login.defs" with the following command:

$ sudo grep -i pass_min_days /etc/login.defs
PASS_MIN_DAYS 1

If the "PASS_MIN_DAYS" parameter value is not "1" or greater or is commented out, this is a finding.

Fix

Configure OL 8 to enforce 24 hours/1 day as the minimum password lifetime.

Add the following line in "/etc/login.defs" (or modify the line to have the required value):

PASS_MIN_DAYS 1

OL 8 user account passwords must have a 60-day maximum password lifetime restriction.

Vulnerability Discussion

Any password, no matter how complex, can eventually be cracked. Therefore, passwords need to be changed periodically. If OL 8 does not limit the lifetime of passwords and force users to change their passwords, there is the risk that OL 8 passwords could be compromised.

Check

Verify that OL 8 enforces a 60-day maximum password lifetime for new user accounts by running the following command:

$ sudo grep -i pass_max_days /etc/login.defs
PASS_MAX_DAYS 60

If the "PASS_MAX_DAYS" parameter value is greater than "60", or commented out, this is a finding.

Fix

Configure OL 8 to enforce a 60-day maximum password lifetime.

Add or modify the following line in the "/etc/login.defs" file:

PASS_MAX_DAYS 60

The OL 8 audit system must take appropriate action when the audit storage volume is full.

Vulnerability Discussion

It is critical that when OL 8 is at risk of failing to process audit logs as required, it takes action to mitigate the failure. Audit processing failures include software/hardware errors; failures in the audit capturing mechanisms; and audit storage capacity being reached or exceeded. Responses to audit failure depend on the nature of the failure mode.

When availability is an overriding concern, other approved actions in response to an audit failure are as follows:

1) If the failure was caused by the lack of audit record storage capacity, OL 8 must continue generating audit records if possible (automatically restarting the audit service if necessary) and overwriting the oldest audit records in a first-in-first-out manner.

2) If audit records are sent to a centralized collection server and communication with this server is lost or the server fails, OL 8 must queue audit records locally until communication is restored or until the audit records are retrieved manually. Upon restoration of the connection to the centralized collection server, action should be taken to synchronize the local audit data with the collection server.

Check

Verify OL 8 takes the appropriate action when the audit storage volume is full with the following command:

$ sudo grep disk_full_action /etc/audit/auditd.conf

disk_full_action = HALT

If the value of the "disk_full_action" option is not "SYSLOG", "SINGLE", or "HALT", or the line is commented out, this is a finding.

Fix

Configure OL 8 to shut down by default upon audit failure (unless availability is an overriding concern).

Add or update the following line ("disk_full_action" can be set to "SYSLOG" or "SINGLE" depending on configuration) in the "/etc/audit/auditd.conf" file:

disk_full_action = HALT

If availability has been determined to be more important, and this decision is documented with the ISSO, configure OL 8 to notify system administration staff and ISSO staff in the event of an audit processing failure by setting the "disk_full_action" to "SYSLOG".

The OL 8 audit system must audit local events.

The OL 8 audit system must protect auditing rules from unauthorized change.

Vulnerability Discussion

Unauthorized disclosure of audit records can reveal system and configuration data to attackers, thus compromising its confidentiality.

Audit information includes all information (e.g., audit records, audit settings, audit reports) needed to successfully audit OL 8 system activity.

In immutable mode, unauthorized users cannot execute changes to the audit system to potentially hide malicious activity and then put the audit rules back. A system reboot would be noticeable and a system administrator could then investigate the unauthorized changes.

Satisfies: SRG-OS-000057-GPOS-00027, SRG-OS-000058-GPOS-00028, SRG-OS-000059-GPOS-00029

Check

Verify the audit system prevents unauthorized changes with the following command:

$ sudo grep "^\s*[^#]" /etc/audit/audit.rules | tail -1

-e 2

If the audit system is not set to be immutable by adding the "-e 2" option to the "/etc/audit/audit.rules", this is a finding.

Fix

Configure the audit system to set the audit rules to be immutable by adding the following line to "/etc/audit/rules.d/audit.rules":

-e 2

Note: Once set, the system must be rebooted for auditing to be changed. It is recommended to add this option as the last step in securing the system.

STIG ID: OL08-00-030180 | SRG: SRG-OS-000037-GPOS-00015 | Severity: medium | CCI: CCI-000130,CCI-000131,CCI-000132,CCI-000133,CCI-000134,CCI-000135,CCI-000154,CCI-000158,CCI-000169,CCI-000172,CCI-001464,CCI-001487,CCI-001814,CCI-001875,CCI-001876,CCI-001877,CCI-001878,CCI-001879,CCI-001880,CCI-001881,CCI-001882,CCI-001889,CCI-001914,CCI-002884 | Vulnerability Id: V-248519 |

Vulnerability Discussion

Without establishing what type of events occurred and their source, location, and outcome, it would be difficult to establish, correlate, and investigate the events leading up to an outage or attack.

Audit record content that may be necessary to satisfy this requirement includes, for example, time stamps, source and destination addresses, user/process identifiers, event descriptions, success/fail indications, filenames involved, and access control or flow control rules invoked.

Associating event types with detected events in OL 8 audit logs provides a means of investigating an attack, recognizing resource utilization or capacity thresholds, or identifying an improperly configured OL 8 system.

Satisfies: SRG-OS-000037-GPOS-00015, SRG-OS-000038-GPOS-00016, SRG-OS-000039-GPOS-00017, SRG-OS-000040-GPOS-00018, SRG-OS-000041-GPOS-00019, SRG-OS-000042-GPOS-00021, SRG-OS-000051-GPOS-00024, SRG-OS-000054-GPOS-00025, SRG-OS-000062-GPOS-00031, SRG-OS-000122-GPOS-00063, SRG-OS-000254-GPOS-00095, SRG-OS-000255-GPOS-00096, SRG-OS-000337-GPOS-00129, SRG-OS-000348-GPOS-00136, SRG-OS-000349-GPOS-00137, SRG-OS-000350-GPOS-00138, SRG-OS-000351-GPOS-00139, SRG-OS-000352-GPOS-00140, SRG-OS-000353-GPOS-00141, SRG-OS-000354-GPOS-00142, SRG-OS-000358-GPOS-00145, SRG-OS-000365-GPOS-00152, SRG-OS-000392-GPOS-00172, SRG-OS-000475-GPOS-00220

Check

Verify the audit service is configured to produce audit records.

Check that the audit service is installed with the following command:

$ sudo yum list installed audit

If the "auditd" package is not installed, this is a finding.

Fix

Configure the audit service to produce audit records containing the information needed to establish when (date and time) an event occurred.

Install the audit service (if the audit service is not already installed) with the following command:

$ sudo yum install audit

OL 8 audit records must contain information to establish what type of events occurred, the source of events, where events occurred, and the outcome of events.

STIG ID: OL08-00-030181 | SRG: SRG-OS-000037-GPOS-00015 | Severity: medium | CCI: CCI-000130,CCI-000131,CCI-000132,CCI-000133,CCI-000134,CCI-000135,CCI-000154,CCI-000158,CCI-000169,CCI-000172,CCI-001464,CCI-001487,CCI-001814,CCI-001875,CCI-001876,CCI-001877,CCI-001878,CCI-001879,CCI-001880,CCI-001881,CCI-001882,CCI-001889,CCI-001914,CCI-002884 | Vulnerability Id: V-248520 |

Vulnerability Discussion

Check

Verify the audit service is configured to produce audit records with the following command:

$ sudo systemctl status auditd.service

auditd.service - Security Auditing Service
Loaded:loaded (/usr/lib/systemd/system/auditd.service; enabled; vendor preset: enabled)
Active: active (running) since Tues 2020-12-11 12:56:56 EST; 4 weeks 0 days ago

If the audit service is not "active" and "running", this is a finding.

Fix

Configure the audit service to produce audit records containing the information needed to establish when (date and time) an event occurred with the following commands:

$ sudo systemctl enable auditd.service

$ sudo systemctl start auditd.service

OL 8 must generate audit records for any use of the "su" command.

Vulnerability Discussion

Check

Verify OL 8 generates audit records for any use of the "su" command by running the following command to check the file system rules in "/etc/audit/audit.rules":

$ sudo grep -iw /usr/bin/su /etc/audit/audit.rules

-a always,exit -F path=/usr/bin/su -F perm=x -F auid>=1000 -F auid!=unset -k privileged-priv_change

If the command does not return a line or the line is commented out, this is a finding.

Note: The "-k" allows for specifying an arbitrary identifier, and the string after it does not need to match the example output above.

Fix

Configure OL 8 to generate audit records for any use of the "su" command by adding or updating the following rule in "/etc/audit/rules.d/audit.rules":

-a always,exit -F path=/usr/bin/su -F perm=x -F auid>=1000 -F auid!=unset -k privileged-priv_change

The audit daemon must be restarted for the changes to take effect. To restart the audit daemon, run the following command:

$ sudo service auditd restart

The OL 8 audit system must be configured to audit any use of the "setxattr", "fsetxattr", "lsetxattr", "removexattr", "fremovexattr", and "lremovexattr" system calls.

OL 8 must generate audit records for any use of the "rename", "unlink", "rmdir", "renameat", and "unlinkat" system calls.

OL 8 must not have the telnet-server package installed.

OL 8 must enable mitigations against processor-based vulnerabilities.

A firewall must be active on OL 8.

Vulnerability Discussion

Check

Verify that "firewalld" is active with the following commands:

$ sudo systemctl is-active firewalld

active

If the "firewalld" package is not "active", ask the System Administrator if another firewall is installed. If no firewall is installed and active this is a finding.

Fix

Configure "firewalld" to protect the operating system with the following commands:

$ sudo systemctl enable firewalld

$ sudo systemctl start firewalld

OL 8 wireless network adapters must be disabled.

Vulnerability Discussion

Without protection of communications with wireless peripherals, confidentiality and integrity may be compromised because unprotected communications can be intercepted and read, altered, or used to compromise the OL 8 operating system.

This requirement applies to wireless peripheral technologies (e.g., wireless mice, keyboards, displays, etc.) used with OL 8 systems. Wireless peripherals (e.g., Wi-Fi/Bluetooth/IR keyboards, mice, and pointing devices and Near Field Communications [NFC]) present a unique challenge by creating an open, unsecured port on a computer. Wireless peripherals must meet DoD requirements for wireless data transmission and be approved for use by the Authorizing Official (AO). Although some wireless peripherals, such as mice and pointing devices, do not ordinarily carry information that need to be protected, modification of communications with these wireless peripherals may be used to compromise the OL 8 operating system. Communication paths outside the physical protection of a controlled boundary are exposed to the possibility of interception and modification.

Protecting the confidentiality and integrity of communications with wireless peripherals can be accomplished by physical means (e.g., employing physical barriers to wireless radio frequencies) or by logical means (e.g., employing cryptographic techniques). If physical means of protection are employed, logical means (cryptography) do not have to be employed, and vice versa. If the wireless peripheral is only passing telemetry data, encryption of the data may not be required.

Satisfies: SRG-OS-000299-GPOS-00117, SRG-OS-000300-GPOS-00118, SRG-OS-000481-GPOS-000481

Check

Verify there are no wireless interfaces configured on the system with the following command.

Note: This requirement is not applicable for systems that do not have physical wireless network radios.

$ sudo nmcli device status

DEVICE TYPE STATE CONNECTION
virbr0 bridge connected virbr0
wlp7s0 wifi connected wifiSSID
enp6s0 ethernet disconnected --
p2p-dev-wlp7s0 wifi-p2p disconnected --
lo loopback unmanaged --
virbr0-nic tun unmanaged --

If a wireless interface is configured and has not been documented and approved by the Information System Security Officer (ISSO), this is a finding.

Fix

Configure the system to disable all wireless network interfaces with the following command:

$ sudo nmcli radio all off

OL 8 Bluetooth must be disabled.

Vulnerability Discussion

Check

If the device or operating system does not have a Bluetooth adapter installed, this requirement is not applicable.

This requirement is not applicable to mobile devices (smartphones and tablets), where the use of Bluetooth is a local AO decision.

Determine if Bluetooth is disabled with the following command:

$ sudo grep -r bluetooth /etc/modprobe.d
/etc/modprobe.d/bluetooth.conf:install bluetooth /bin/false

If the command does not return any output or the line is commented out and the collaborative computing device has not been authorized for use, this is a finding.

Verify the operating system disables the ability to use Bluetooth with the following command:

$ sudo grep -r bluetooth /etc/modprobe.d | grep -i "blacklist" | grep -v "^#"
blacklist bluetooth

If the command does not return any output or the output is not "blacklist bluetooth", and use of Bluetooth is not documented with the Information System Security Officer (ISSO) as an operational requirement, this is a finding.

Fix

Configure the operating system to disable the Bluetooth adapter when not in use.

Build or modify the "/etc/modprobe.d/bluetooth.conf" file with the following line:

install bluetooth /bin/false

Disable the ability to use the Bluetooth kernel module.

$ sudo vi /etc/modprobe.d/blacklist.conf

Add or update the line:

blacklist bluetooth

Reboot the system for the settings to take effect.

OL 8 must mount "/dev/shm" with the "nodev" option.

A firewall must be able to protect against or limit the effects of denial-of-service (DoS) attacks by ensuring OL 8 can implement rate-limiting measures on impacted network interfaces.

Vulnerability Discussion

DoS is a condition when a resource is not available for legitimate users. When this occurs, the organization either cannot accomplish its mission or must operate at degraded capacity.

This requirement addresses the configuration of OL 8 to mitigate the impact of DoS attacks that have occurred or are ongoing on system availability. For each system, known and potential DoS attacks must be identified and solutions for each type implemented. A variety of technologies exists to limit or, in some cases, eliminate the effects of DoS attacks (e.g., limiting processes or establishing memory partitions). Employing increased capacity and bandwidth, combined with service redundancy, may reduce the susceptibility to some DoS attacks.

Since version 0.6.0, "firewalld" has incorporated "nftables" as its backend support. Using the limit statement in "nftables" can help to mitigate DoS attacks.

Satisfies: SRG-OS-000142-GPOS-00071, SRG-OS-000298-GPOS-00116, SRG-OS-000420-GPOS-00186

Check

Verify "nftables" is configured to allow rate limits on any connection to the system with the following command.

Verify "firewalld" has "nftables" set as the default backend:

$ sudo grep -i firewallbackend /etc/firewalld/firewalld.conf

# FirewallBackend
FirewallBackend=nftables

If the "nftables" is not set as the "firewallbackend" default, this is a finding.

Fix

Configure "nftables" to be the default "firewallbackend" for "firewalld" by adding or editing the following line in "/etc/firewalld/firewalld.conf":

FirewallBackend=nftables

Establish rate-limiting rules based on organization-defined types of DoS attacks on impacted network interfaces.

All OL 8 networked systems must have SSH installed.

OL 8 must not enable IPv4 packet forwarding unless the system is a router.

Vulnerability Discussion

Routing protocol daemons are typically used on routers to exchange network topology information with other routers. If this software is used when not required, system network information may be unnecessarily transmitted across the network.

The sysctl --system command will load settings from all system configuration files. All configuration files are sorted by their filename in lexicographic order, regardless of which of the directories they reside in. If multiple files specify the same option, the entry in the file with the lexicographically latest name will take precedence. Files are read from directories in the following list from top to bottom. Once a file of a given filename is loaded, any file of the same name in subsequent directories is ignored.
/etc/sysctl.d/*.conf
/run/sysctl.d/*.conf
/usr/local/lib/sysctl.d/*.conf
/usr/lib/sysctl.d/*.conf
/lib/sysctl.d/*.conf
/etc/sysctl.conf

Check

Verify OL 8 is not performing IPv4 packet forwarding, unless the system is a router.

Check that IPv4 forwarding is disabled using the following command:

$ sudo sysctl net.ipv4.conf.all.forwarding

net.ipv4.conf.all.forwarding = 0

If the IPv4 forwarding value is not "0" and is not documented with the Information System Security Officer (ISSO) as an operational requirement, this is a finding.

Check that the configuration files are present to enable this network parameter:

$ sudo grep -r net.ipv4.conf.all.forwarding /run/sysctl.d/*.conf /usr/local/lib/sysctl.d/*.conf /usr/lib/sysctl.d/*.conf /lib/sysctl.d/*.conf /etc/sysctl.conf /etc/sysctl.d/*.conf

/etc/sysctl.d/99-sysctl.conf: net.ipv4.conf.all.forwarding = 0

If "net.ipv4.conf.all.forwarding" is not set to "0", is missing or commented out, this is a finding.

If conflicting results are returned, this is a finding.

Fix

Configure OL 8 to not allow IPv4 packet forwarding unless the system is a router.

Add or edit the following line in a system configuration file, in the "/etc/sysctl.d/" directory:

net.ipv4.conf.all.forwarding=0

Remove any configurations that conflict with the above from the following locations:
/run/sysctl.d/*.conf
/usr/local/lib/sysctl.d/*.conf
/usr/lib/sysctl.d/*.conf
/lib/sysctl.d/*.conf
/etc/sysctl.conf
/etc/sysctl.d/*.conf

Load settings from all system configuration files with the following command:

$ sudo sysctl --system

OL 8 must not enable IPv6 packet forwarding unless the system is a router.

Vulnerability Discussion

Check

Verify OL 8 is not performing IPv6 packet forwarding unless the system is a router.

Note: If IPv6 is disabled on the system, this requirement is Not Applicable.

Determine if IPv6 forwarding is disabled using the following commands:

$ sudo sysctl net.ipv6.conf.all.forwarding

net.ipv6.conf.all.forwarding = 0

If the IPv6 forwarding value is "1" and is not documented with the Information System Security Officer (ISSO) as an operational requirement, this is a finding.

Check that the configuration files are present to enable this network parameter.

$ sudo grep -r net.ipv6.conf.all.forwarding /run/sysctl.d/*.conf /usr/local/lib/sysctl.d/*.conf /usr/lib/sysctl.d/*.conf /lib/sysctl.d/*.conf /etc/sysctl.conf /etc/sysctl.d/*.conf

/etc/sysctl.d/99-sysctl.conf: net.ipv6.conf.all.forwarding = 0

If "net.ipv6.conf.all.forwarding" is not set to "0", is missing or commented out, this is a finding.

If conflicting results are returned, this is a finding.

Fix

Configure OL 8 to not allow IPv6 packet forwarding unless the system is a router with the following command:

$ sudo sysctl -w net.ipv6.conf.all.forwarding=0

Remove any configurations that conflict with the above from the following locations:
/run/sysctl.d/*.conf
/usr/local/lib/sysctl.d/*.conf
/usr/lib/sysctl.d/*.conf
/lib/sysctl.d/*.conf
/etc/sysctl.conf
/etc/sysctl.d/*.conf

If "0" is not the system's default value, add or update the following lines in "/etc/sysctl.conf" or in the appropriate file under "/etc/sysctl.d":

net.ipv6.conf.all.forwarding=0

OL 8 must not accept router advertisements on all IPv6 interfaces.

Vulnerability Discussion

Routing protocol daemons are typically used on routers to exchange network topology information with other routers. If this software is used when not required, system network information may be unnecessarily transmitted across the network.

An illicit router advertisement message could result in a man-in-the-middle attack.

The sysctl --system command will load settings from all system configuration files. All configuration files are sorted by their filename in lexicographic order, regardless of which of the directories they reside in. If multiple files specify the same option, the entry in the file with the lexicographically latest name will take precedence. Files are read from directories in the following list from top to bottom. Once a file of a given filename is loaded, any file of the same name in subsequent directories is ignored.
/etc/sysctl.d/*.conf
/run/sysctl.d/*.conf
/usr/local/lib/sysctl.d/*.conf
/usr/lib/sysctl.d/*.conf
/lib/sysctl.d/*.conf
/etc/sysctl.conf

Check

Verify OL 8 does not accept router advertisements on all IPv6 interfaces unless the system is a router.

Note: If IPv6 is disabled on the system, this requirement is not applicable.

Determine if router advertisements are not accepted by using the following command:

$ sudo sysctl net.ipv6.conf.all.accept_ra

net.ipv6.conf.all.accept_ra = 0

If the "accept_ra" value is not "0" and is not documented with the Information System Security Officer (ISSO) as an operational requirement, this is a finding.

Check that the configuration files are present to enable this network parameter.

$ sudo grep -r net.ipv6.conf.all.accept_ra /run/sysctl.d/*.conf /usr/local/lib/sysctl.d/*.conf /usr/lib/sysctl.d/*.conf /lib/sysctl.d/*.conf /etc/sysctl.conf /etc/sysctl.d/*.conf

/etc/sysctl.d/99-sysctl.conf: net.ipv6.conf.all.accept_ra = 0

If "net.ipv6.conf.all.accept_ra" is not set to "0", is missing or commented out, this is a finding.

If conflicting results are returned, this is a finding.

Fix

Configure the system to not accept router advertisements on all IPv6 interfaces unless the system is a router with the following commands:

$ sudo sysctl -w net.ipv6.conf.all.accept_ra=0

Remove any configurations that conflict with the above from the following locations:
/run/sysctl.d/*.conf
/usr/local/lib/sysctl.d/*.conf
/usr/lib/sysctl.d/*.conf
/lib/sysctl.d/*.conf
/etc/sysctl.conf
/etc/sysctl.d/*.conf

If "0" is not the system's default value, add or update the following lines in the appropriate file under "/etc/sysctl.d":

net.ipv6.conf.all.accept_ra=0

OL 8 must not accept router advertisements on all IPv6 interfaces by default.

OL 8 must disable the use of user namespaces.