Vulnerability Discussion

If SSHD is enabled, it must be configured to limit the Ciphers, HostbasedAcceptedAlgorithms, HostKeyAlgorithms, KexAlgorithms, MACs, PubkeyAcceptedAlgorithms, CASignatureAlgorithms to algorithms that are FIPS-140 validated.

FIPS 140-2/140-3 is the current standard for validating that mechanisms used to access cryptographic modules use authentication that meets federal requirements.

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

NOTE: For more information on FIPS compliance with the version of SSHD 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-000393-GPOS-00173, SRG-OS-000394-GPOS-00174, SRG-OS-000396-GPOS-00176, SRG-OS-000424-GPOS-00188, SRG-OS-000478-GPOS-00223

Check

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

fips_sshd_config=("Ciphers aes128-gcm@openssh.com" "HostbasedAcceptedAlgorithms ecdsa-sha2-nistp256,ecdsa-sha2-nistp256-cert-v01@openssh.com" "HostKeyAlgorithms ecdsa-sha2-nistp256-cert-v01@openssh.com,sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp256,sk-ecdsa-sha2-nistp256@openssh.com" "KexAlgorithms ecdh-sha2-nistp256" "MACs hmac-sha2-256-etm@openssh.com,hmac-sha2-256" "PubkeyAcceptedAlgorithms ecdsa-sha2-nistp256,ecdsa-sha2-nistp256-cert-v01@openssh.com,sk-ecdsa-sha2-nistp256-cert-v01@openssh.com" "CASignatureAlgorithms ecdsa-sha2-nistp256,sk-ecdsa-sha2-nistp256@openssh.com")
total=0
for config in $fips_sshd_config; do
total=$(expr $(/usr/sbin/sshd -G | /usr/bin/grep -i -c "$config") + $total)
done

echo $total

If the result is not "7", this is a finding.

Fix

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

/bin/ln -fs /etc/ssh/crypto/fips.conf /etc/ssh/crypto.conf