Title

The Red Hat Enterprise Linux operating system SSH server must be configured to use only FIPS-validated key exchange algorithms. (Cat II impact)

Discussion

The use of FIPS-validated cryptographic algorithms is enforced by enabling kernel FIPS mode. In the event that kernel FIPS mode is disabled, the use of nonvalidated cryptographic algorithms will be permitted systemwide. The SSH server configuration must manually define only FIPS-validated key exchange algorithms to prevent the use of nonvalidated algorithms.

Check Content

Verify that the SSH server is configured to use only FIPS-validated key exchange algorithms: $ sudo grep -i kexalgorithms /etc/ssh/sshd_config KexAlgorithms ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256 If "KexAlgorithms" is not configured, is commented out, or does not contain only the algorithms "ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256" in exact order, this is a finding.

Fix Text

Configure the SSH server to use only FIPS-validated key exchange algorithms by adding or modifying the following line in "/etc/ssh/sshd_config": KexAlgorithms ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256 Restart the "sshd" service for changes to take effect: $ sudo systemctl restart sshd

Additional Identifiers

Rule ID: SV-255925r880749_rule

Vulnerability ID: V-255925

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.