macos_security/rules/os/os_sshd_fips_compliant.yaml

id: os_sshd_fips_compliant
title: Limit SSHD to FIPS Compliant Connections
discussion: |
  If SSHD is enabled then it _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 SSHD 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_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
result:
  integer: 7
fix: |
  [source,bash]
  ----
  if [ -f /etc/ssh/crypto.conf ] && /usr/bin/grep -q "Include /etc/ssh/crypto.conf" /etc/ssh/sshd_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/sshd_config | /usr/bin/tr -d '*')

  if [[ -z $include_dir ]]; then
    /usr/bin/sed -i.bk "1s/.*/Include \/etc\/ssh\/sshd_config.d\/\*/" /etc/ssh/sshd_config
  fi
  
  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")
  sshd_config=$(/usr/sbin/sshd -G)
  for config in $fips_sshd_config; do
    if ! echo $sshd_config | /usr/bin/grep -q -i "$config" 2>/dev/null; then
      /usr/bin/grep -qxF "$config" "${include_dir}01-mscp-sshd.conf" 2>/dev/null || echo "$config" >> "${include_dir}01-mscp-sshd.conf"
    fi
  done

  for file in $(ls ${include_dir}); do
    if [[ "$file" == "100-macos.conf" ]]; then
        continue
    fi
    if [[ "$file" == "01-mscp-sshd.conf" ]]; then
        break
    fi
    /bin/mv ${include_dir}${file} ${include_dir}20-${file}
  done
  ----
references:
  cce:
    - CCE-95310-9
  cci:
    - CCI-000068
    - CCI-000803
    - CCI-001453
    - CCI-002421
    - CCI-002450
    - CCI-002890
    - CCI-003123    
  800-53r5:
    - AC-17(2)
    - IA-7
    - SC-13
    - SC-8(1)
  800-53r4:
    - AC-17(2)
    - IA-7
    - SC-8(1)
    - SC-13
    - MA-4(6)
  srg:
    - SRG-OS-000250-GPOS-00093
    - SRG-OS-000120-GPOS-00061
    - SRG-OS-000424-GPOS-00188
    - SRG-OS-000394-GPOS-00174
    - SRG-OS-000478-GPOS-00223
    - SRG-OS-000033-GPOS-00014
    - SRG-OS-000393-GPOS-00173
    - SRG-OS-000396-GPOS-00176
  disa_stig:
    - APPL-26-000054
  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:
ddm_info:
  declarationtype: com.apple.configuration.services.configuration-files
  service: com.apple.sshd
  config_file: sshd_config
  configuration_key: file
  configuration_value: |
    Ciphers aes128-gcm@openssh.com
    HostbasedAcceptedAlgorithms ecdsa-sha2-nistp256,ecdsa-sha2-nistp256-cert-v01@openssh.com
    HostKeyAlgorithms ecdsa-sha2-nistp256,ecdsa-sha2-nistp256-cert-v01@openssh.com
    KexAlgorithms ecdh-sha2-nistp256
    MACs hmac-sha2-256
    PubkeyAcceptedAlgorithms ecdsa-sha2-nistp256,ecdsa-sha2-nistp256-cert-v01@openssh.com
    CASignatureAlgorithms ecdsa-sha2-nistp256