metadata/service/server/cis/cis-5-2-11.yml

# 5.2.11 Ensure only approved MAC algorithms are used (Scored)
#
# Profile Applicability
# ---------------------
# - Level 1 - Server
# - Level 1 - Workstation
#
# Description
# -----------
# This variable limits the types of MAC algorithms that SSH can use during communication.
#
# Rationale
# ---------
# MD5 and 96-bit MAC algorithms are considered weak and have been shown to increase
# exploitability in SSH downgrade attacks. Weak algorithms continue to have a great deal of
# attention as a weak spot that can be exploited with expanded computing power. An
# attacker that breaks the algorithm could take advantage of a MiTM position to decrypt the
# SSH tunnel and capture credentials and information
#
# Audit
# -----
# Run the following command and verify that output does not contain any unlisted MAC
# algorithms:
#
#   # grep "MACs" /etc/ssh/sshd_config
#   MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,
#   umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,umac-128@openssh.com,
#   curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256
#
# Remediation
# -----------
# Edit the /etc/ssh/sshd_config file to set the parameter as follows:
#
#   MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,
#   umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,umac-128@openssh.com

parameters:
  openssh:
    server:
      mac_algorithms:
        hmac-sha2-512-etm@openssh.com:
          enabled: True
        hmac-sha2-256-etm@openssh.com:
          enabled: True
        umac-128-etm@openssh.com:
          enabled: True
        hmac-sha2-512:
          enabled: True
        hmac-sha2-256:
          enabled: True
        umac-128@openssh.com:
          enabled: True