Title

Ubuntu 24.04 LTS must configure the SSH daemon to use FIPS 140-3 approved ciphers to prevent the unauthorized disclosure of information and/or detect changes to information during transmission. (Cat II impact)

Discussion

Without cryptographic integrity protections, information can be altered by unauthorized users without detection. Remote access (e.g., RDP) is access to DOD nonpublic information systems by an authorized user (or an information system) communicating through an external, nonorganization-controlled network. Remote access methods include, for example, dial-up, broadband, and wireless. Nonlocal maintenance and diagnostic activities are those activities conducted by individuals communicating through a network, either an external network (e.g., the internet) or an internal network. Local maintenance and diagnostic activities are those activities carried out by individuals physically present at the information system or information system component and not communicating across a network connection. Encrypting information for transmission protects information from unauthorized disclosure and modification. Cryptographic mechanisms implemented to protect information integrity include, for example, cryptographic hash functions that have common application in digital signatures, checksums, and message authentication codes. Satisfies: SRG-OS-000033-GPOS-00014, SRG-OS-000394-GPOS-00174, SRG-OS-000424-GPOS-00188

Check Content

Verify that the SSH daemon is configured to implement only FIPS-approved algorithms with the following command: $ sudo grep -r 'Ciphers' /etc/ssh/sshd_config* Ciphers aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes128-ctr If any ciphers other than "Ciphers aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes128-ctr" are listed, the "Ciphers" keyword is missing, or the returned line is commented out, or if multiple conflicting ciphers are returned, this is a finding.

Fix Text

Configure Ubuntu 24.04 LTS to allow the SSH daemon to only implement FIPS-approved algorithms. Add the following line (or modify the line to have the required value) to the "/etc/ssh/sshd_config" file (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): Ciphers aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes128-ctr Restart the "sshd" service for changes to take effect: $ sudo systemctl restart sshd

Additional Identifiers

Rule ID: SV-270667r1067107_rule

Vulnerability ID: V-270667

Group Title: SRG-OS-000033-GPOS-00014

Expert Comments

CCIs tied to check.

Controls tied to check. These are derived from the CCIs shown above.