Title

SLEM 5 SSH server must be configured to use only FIPS 140-2/140-3 validated key exchange algorithms. (Cat I impact)

Discussion

Without cryptographic integrity protections provided by FIPS 140-2/140-3 validated cryptographic algorithms, information can be viewed and altered by unauthorized users without detection. The system will attempt to use the first algorithm presented by the client that matches the server list. Listing the values "strongest to weakest" is a method to ensure the use of the strongest algorithm available to secure the SSH connection.

Check Content

Verify that the SSH server is configured to use only FIPS 140-2/140-3 validated key exchange algorithms with the following command: > sudo /usr/sbin/sshd -dd 2>&1 | awk '/filename/ {print $4}' | tr -d '\r' | tr '\n' ' ' | xargs sudo grep -iH '^\s*kexalgorithms' KexAlgorithms ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256 If "KexAlgorithms" does not contain the list of algorithms in the exact order, is commented out, missing, or conflicting results are returned, this is a finding.

Fix Text

Configure the SSH server to use only FIPS 140-2/140-3 validated key exchange algorithms. Add or modify the following line in the "/etc/ssh/sshd_config" file: KexAlgorithms ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256 Restart the SSH daemon for changes to take effect: > sudo systemctl restart sshd.service

Additional Identifiers

Rule ID: SV-261336r996472_rule

Vulnerability ID: V-261336

Group Title: SRG-OS-000250-GPOS-00093

Expert Comments

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