id: os_ssh_fips_compliant
title: Limit SSH to FIPS Compliant Connections
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.
check: |
  fips_ssh_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
  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 $ret
result:
  string: "pass"
fix: |
  [source,bash]
  ----
  if [ -f /etc/ssh/crypto.conf ] && /usr/bin/grep -q "Include /etc/ssh/crypto.conf" /etc/ssh/ssh_config.d/100-macos.conf 2>/dev/null; then
    /bin/ln -fs /etc/ssh/crypto/fips.conf /etc/ssh/crypto.conf
  fi
  include_dir=$(/usr/bin/awk '/^Include/ {print $2}' /etc/ssh/ssh_config | /usr/bin/tr -d '*')
  
  fips_ssh_config=("Ciphers 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")
  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
  ----   
references:
  cce:
    - CCE-95304-2
  cci:
    - CCI-000068
    - CCI-000803
    - CCI-001453
    - CCI-002421
    - CCI-002450
  800-53r5:
    - AC-17(2)
    - IA-7
    - SC-13
    - SC-8(1)
  800-53r4:
    - AC-17(2)
    - IA-7
    - SC-8(1)
    - SC-13
  srg:
    - SRG-OS-000250-GPOS-00093
    - SRG-OS-000120-GPOS-00061
    - SRG-OS-000424-GPOS-00188
    - SRG-OS-000478-GPOS-00223
    - SRG-OS-000033-GPOS-00014
    - SRG-OS-000396-GPOS-00176
  disa_stig:
    - APPL-26-000057
  800-171r3:
    - 03.13.08
    - 03.13.11
  cmmc:
    - AC.L2-3.1.13
    - MP.L2-3.8.6
    - SC.L2-3.13.8
    - SC.L2-3.13.11
macOS:
  - '26.0'
tags:
  - 800-53r5_moderate
  - 800-53r5_high
  - 800-53r5_low
  - 800-53r4_low
  - 800-53r4_moderate
  - 800-53r4_high
  - 800-171
  - cnssi-1253_low
  - cnssi-1253_high
  - cmmc_lvl2
  - stig
  - cnssi-1253_moderate
severity: high
mobileconfig: false
mobileconfig_info:
