UBTU-24-100850 - Ubuntu 24.04 LTS must configure the SSH client to use FIPS 140-3 approved ciphers to prevent the unauthorized disclosure of information and/or detect changes to information during transmission.

Information

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.

By specifying a cipher list with the order of ciphers being in a "strongest to weakest" orientation, the system will automatically attempt to use the strongest cipher for securing SSH connections.

Solution

Configure the Ubuntu 24.04 LTS SSH client to use only ciphers employing FIPS 140-3 approved algorithms by updating the "/etc/ssh/ssh_config" file with the following line:

Ciphers [email protected],[email protected],aes256-ctr,aes128-ctr

Restart the "ssh" service for changes to take effect:

$ sudo systemctl restart ssh

See Also

https://dl.dod.cyber.mil/wp-content/uploads/stigs/zip/U_CAN_Ubuntu_24-04_LTS_V1R1_STIG.zip

Item Details

Category: ACCESS CONTROL

References: 800-53|AC-17(2), CAT|II, CCI|CCI-001453, Rule-ID|SV-270670r1067115_rule, STIG-ID|UBTU-24-100850, Vuln-ID|V-270670

Plugin: Unix

Control ID: ca9a7ff00c689c0923db79e7d8caee19681a5b71bf0a9d39e2080bfd47aea1c0