os_ssh_fips_compliant Limit SSH to FIPS Compliant Connections
All changes in this version
Title
Limit SSH to FIPS Compliant Connections
Control
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]")
total=0
ret="pass"
for config in $fips_ssh_config; do
if [[ "$ret" == "fail" ]]; then
break
fi
for u in $(/usr/bin/dscl . list /users shell | /usr/bin/egrep -v '(^_)|(root)|(/usr/bin/false)' | /usr/bin/awk '{print $1}'); do
sshCheck=$(/usr/bin/sudo -u $u /usr/bin/ssh -G . | /usr/bin/grep -ci "$config")
if [[ "$sshCheck" == "0" ]]; then
ret="fail"
break
fi
done
done
echo $ret
Discussion
SSH _MUST_ be configured to limit the Ciphers, HostbasedAcceptedAlgorithms, HostKeyAlgorithms, KexAlgorithms, MACs, PubkeyAcceptedAlgorithms, CASignatureAlgorithms to algorithms that are FIPS 140 validated.
FIPS 140-3 is the current standard for validating that mechanisms used to access cryptographic modules utilize authentication that meet federal requirements.
Operating systems utilizing encryption _MUST_ use FIPS validated mechanisms for authenticating to cryptographic modules.
NOTE: For more information on FIPS compliance with the version of SSH included in the macOS, the manual page apple_ssh_and_fips has additional information.
NOTE: On macOS 15.2 and higher the SSH configuration can be reset to the macOS default by running /usr/libexec/reset-ssh-configuration.
Related controls
ac-17.2, ia-7, sc-13, sc-8.1
Fix
[source,bash]
----
if [ -f /etc/ssh/crypto.conf ] && /usr/bin/grep -q "Include /etc/ssh/crypto.conf" /etc/ssh/ssh_config.d/100-macos.conf 2>/dev/null; then
/bin/ln -fs /etc/ssh/crypto/fips.conf /etc/ssh/crypto.conf
fi
include_dir=$(/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
----