APPL-26-000057 - The macOS system must limit SSH to FIPS-compliant connections.

Information

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

FIPS 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 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

Solution

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

if [ -f /etc/ssh/crypto.conf ] && /usr/bin/grep -q "Include /etc/ssh/crypto.conf" /etc/ssh/ssh_config.d/100-macos.conf 2>/dev/null; then
/bin/ln -fs /etc/ssh/crypto/fips.conf /etc/ssh/crypto.conf
fi
include_dir=$(/usr/bin/awk '/^Include/ {print $2}' /etc/ssh/ssh_config | /usr/bin/tr -d '*')

fips_ssh_config=("Ciphers [email protected]" "HostbasedAcceptedAlgorithms ecdsa-sha2-nistp256,[email protected]" "HostKeyAlgorithms [email protected],[email protected],ecdsa-sha2-nistp256,[email protected]" "KexAlgorithms ecdh-sha2-nistp256" "MACs [email protected],hmac-sha2-256" "PubkeyAcceptedAlgorithms ecdsa-sha2-nistp256,[email protected],[email protected]" "CASignatureAlgorithms ecdsa-sha2-nistp256,[email protected]")
for ssh_config in $fips_ssh_config; do
ssh_setting=$(echo $ssh_config | /usr/bin/cut -d " " -f1)
/usr/bin/grep -qEi "^$ssh_setting" "${include_dir}01-mscp-ssh.conf" && /usr/bin/sed -i "" "s/^$ssh_setting.*/${ssh_config}/" "${include_dir}01-mscp-ssh.conf" || echo "$ssh_config" >> "${include_dir}01-mscp-ssh.conf"
for u in $(/usr/bin/dscl . list /users shell | /usr/bin/egrep -v '(^_)|(root)|(/usr/bin/false)' | /usr/bin/awk '{print $1}'); do
config=$(/usr/bin/sudo -u $u /usr/bin/ssh -Gv . 2>&1)
configfiles=$(echo "$config" | /usr/bin/awk '/Reading configuration data/ {print $NF}'| /usr/bin/tr -d '\r')
configarray=( ${(f)configfiles} )
if ! echo $config | /usr/bin/grep -q -i "$ssh_config" ; then
for c in $configarray; do
if [[ "$c" == "/etc/ssh/crypto.conf" ]]; then
continue
fi

/usr/bin/sudo -u $u /usr/bin/grep -qEi "^$ssh_setting" "$c" && /usr/bin/sed -i "" "s/^$ssh_setting.*/${ssh_config}/I" "$c"
if [[ "$c" =~ ".ssh/config" ]]; then
if /usr/bin/grep -qEi "$ssh_setting" "$c" 2> /dev/null; then
old_file=$(cat ~$u/.ssh/config)
echo "$ssh_config" > ~$u/.ssh/config
echo "$old_file" >> ~$u/.ssh/config
fi
fi
done
fi
done
done

Item Details

Audit Name: DISA Apple macOS 26 Tahoe STIG v1r1

Category: ACCESS CONTROL, IDENTIFICATION AND AUTHENTICATION, SYSTEM AND COMMUNICATIONS PROTECTION

Plugin: Unix

Control ID: ef7cc99bdb2d17405e6185a6175b8d7643cc4fb88ae70bc0f1cb34f1f32367dd

Detections

Analytics

APPL-26-000057 - The macOS system must limit SSH to FIPS-compliant connections.

Information

Solution

See Also

Item Details