Vulnerability Discussion

Display of a standardized and approved use notification before granting access to the publicly accessible operating system ensures privacy and security notification verbiage used is consistent with applicable federal laws, Executive Orders, directives, policies, regulations, standards, and guidance.

System use notifications are required only for access via logon interfaces with human users and are not required when such human interfaces do not exist.

The banner must be formatted in accordance with applicable DOD policy. Use the following verbiage for operating systems that can accommodate banners of 1300 characters:

"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."

Use the following verbiage for operating systems that have severe limitations on the number of characters that can be displayed in the banner:

"I've read (literal ampersand) consent to terms in IS user agreem't."

Satisfies: SRG-OS-000023-GPOS-00006, SRG-OS-000228-GPOS-00088

Check

Verify Ubuntu 22.04 LTS displays the Standard Mandatory DOD Notice and Consent Banner before granting access to Ubuntu 22.04 LTS via an SSH logon by using the following command:

$ sudo /usr/sbin/sshd -dd 2>&1 | awk '/filename/ {print $4}' | tr -d '\r' | tr '\n' ' ' | xargs sudo grep -iH 'banner'
/etc/ssh/sshd_config:Banner /etc/issue.net

The command will return the banner option along with the name of the file that contains the SSH banner. If the line is commented out, missing, or conflicting results are returned, this is a finding.

Verify the specified banner file matches the Standard Mandatory DOD Notice and Consent Banner exactly:

$ cat /etc/issue.net
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.

If the banner text does not match the Standard Mandatory DOD Notice and Consent Banner exactly, this is a finding.

Fix

Set the parameter Banner in "/etc/ssh/sshd_config" to point to the "/etc/issue.net" file:

$ sudo sed -i '/^Banner/d' /etc/ssh/sshd_config
$ sudo sed -i '$aBanner /etc/issue.net' /etc/ssh/sshd_config

Replace the text in "/etc/issue.net" with the Standard Mandatory DOD Notice and Consent Banner:

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.

Restart the SSH daemon for the changes to take effect and then signal the SSH server to reload the configuration file:

$ sudo systemctl -s SIGHUP kill sshd