Vulnerability Discussion

SSH must be configured to limit the Ciphers, HostbasedAcceptedAlgorithms, HostKeyAlgorithms, KexAlgorithms, MACs, PubkeyAcceptedAlgorithms, CASignatureAlgorithms to algorithms that are FIPS 140 validated.

FIPS 140-2 is the current standard for validating that mechanisms used to access cryptographic modules utilize authentication that meet federal requirements.

Operating systems utilizing encryption must use FIPS-validated mechanisms for authenticating to cryptographic modules.

Note: For more information on FIPS compliance with the version of SSH included in the macOS, the manual page apple_ssh_and_fips has additional information.

Satisfies: SRG-OS-000033-GPOS-00014,SRG-OS-000120-GPOS-00061,SRG-OS-000250-GPOS-00093,SRG-OS-000396-GPOS-00176,SRG-OS-000424-GPOS-00188,SRG-OS-000478-GPOS-00223

Check

Verify the macOS system is configured to limit SSH to FIPS-compliant connections with the following command:

fips_ssh_config="Host *
Ciphers [email protected]
HostbasedAcceptedAlgorithms ecdsa-sha2-nistp256,[email protected]
HostKeyAlgorithms ecdsa-sha2-nistp256,[email protected]
KexAlgorithms ecdh-sha2-nistp256
MACs hmac-sha2-256
PubkeyAcceptedAlgorithms ecdsa-sha2-nistp256,[email protected]
CASignatureAlgorithms ecdsa-sha2-nistp256"
/usr/bin/grep -c "$fips_ssh_config" /etc/ssh/ssh_config.d/fips_ssh_config

If the result is not "8", this is a finding.

Fix

Configure the macOS system to limit SSH to FIPS-compliant connections with the following command:

fips_ssh_config="Host *
Ciphers [email protected]
HostbasedAcceptedAlgorithms ecdsa-sha2-nistp256,[email protected]
HostKeyAlgorithms ecdsa-sha2-nistp256,[email protected]
KexAlgorithms ecdh-sha2-nistp256
MACs hmac-sha2-256
PubkeyAcceptedAlgorithms ecdsa-sha2-nistp256,[email protected]
CASignatureAlgorithms ecdsa-sha2-nistp256"
/bin/echo "${fips_ssh_config}" > /etc/ssh/ssh_config.d/fips_ssh_config