Vulnerability Discussion

SSH must be configured to display a policy banner.

Displaying a standardized and approved use notification before granting access to the operating system ensures that users are provided with privacy and security notification verbiage that is consistent with applicable federal laws, Executive Orders, directives, policies, regulations, standards, and guidance.

System use notifications are required only for access via login interfaces with human users and are not required when such human interfaces do not exist.

NOTE: /etc/ssh/sshd_config will be automatically modified to its original state following any update or major upgrade to the operating system.

Satisfies: SRG-OS-000023-GPOS-00006, SRG-OS-000024-GPOS-00007

Check

Verify the macOS system is configured to display the contents of "/etc/banner" before granting access to the system with the following command:

/usr/sbin/sshd -G | /usr/bin/grep -c "^banner /etc/banner"

If the command does not return "1", this is a finding.

Fix

Configure the macOS system to display the contents of "/etc/banner" before granting access to the system with the following command:

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

/usr/bin/grep -qxF 'banner /etc/banner' "${include_dir}01-mscp-sshd.conf" 2>/dev/null || echo "banner /etc/banner" >> "${include_dir}01-mscp-sshd.conf"

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