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UBTU-22-255055 Ubuntu 22.04 LTS must configure the SSH daemon to use Message Authentication Codes (MACs) employing FIPS 140-3-approved cryptographic hashes to prevent the unauthorized disclosure of information and/or detect changes to information during transmission.

DISA STIG library V2R10
All changes in this version
first version loaded CAT II

Maps to AC-17(2), MA-4(6), SC-8(1) via CCI-001453, CCI-002421, CCI-002890

Title

Ubuntu 22.04 LTS must configure the SSH daemon to use Message Authentication Codes (MACs) employing FIPS 140-3-approved cryptographic hashes to prevent the unauthorized disclosure of information and/or detect changes to information during transmission.

Control

Verify the SSH server is configured to only use MACs that employ FIPS 140-3 approved ciphers 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 'macs' /etc/ssh/sshd_config:MACs hmac-sha2-512,[email protected],hmac-sha2-256,[email protected] If "MACs" does not contain only the hashes "hmac-sha2-512,[email protected],hmac-sha2-256,[email protected]" in exact order, is commented out, is missing, or conflicting results are returned, this is a finding.

Discussion

Without cryptographic integrity protections, information can be altered by unauthorized users without detection. Remote access (e.g., RDP) is access to DoW nonpublic information systems by an authorized user (or an information system) communicating through an external, non-organization-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, which have common application in digital signatures, checksums, and message authentication codes. Satisfies: SRG-OS-000250-GPOS-00093, SRG-OS-000393-GPOS-00173, SRG-OS-000424-GPOS-00188

Related controls

CCI-001453, CCI-002421, CCI-002890

Fix

Configure the SSH server to only use MACs that employ FIPS 140-3 approved hashes. Add or modify the following line in the "/etc/ssh/sshd_config" file: MACs hmac-sha2-512,[email protected],hmac-sha2-256,[email protected] Restart the SSH server for the changes to take effect: $ sudo systemctl reload sshd.service