Configure SSH to use System Crypto Policy

Description

Crypto Policies provide a centralized control over crypto algorithms usage of many packages. SSH is supported by crypto policy, but the SSH configuration may be set up to ignore it. To check that Crypto Policies settings are configured correctly, ensure that the CRYPTO_POLICY variable is either commented or not set at all in the /etc/sysconfig/sshd.

Rationale

Overriding the system crypto policy makes the behavior of the SSH service violate expectations, and makes system configuration more fragmented.

Remediation

Shell script

The following script can be run on the host to remediate the issue.

#!/bin/bash

# Remediation is applicable only in certain platforms
if rpm --quiet -q kernel-core; then

SSH_CONF="/etc/sysconfig/sshd"

sed -i "/^\s*CRYPTO_POLICY.*$/Id" $SSH_CONF

else
    >&2 echo 'Remediation is not applicable, nothing was done'
fi

Ansible playbook

The following playbook can be run with Ansible to remediate the issue.

- name: Gather the package facts
  package_facts:
    manager: auto
  tags:
  - CCE-80939-2
  - DISA-STIG-RHEL-08-010287
  - NIST-800-53-AC-17(2)
  - NIST-800-53-AC-17(a)
  - NIST-800-53-CM-6(a)
  - NIST-800-53-MA-4(6)
  - NIST-800-53-SC-13
  - PCI-DSS-Req-2.2
  - PCI-DSSv4-2.2
  - PCI-DSSv4-2.2.7
  - configure_ssh_crypto_policy
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required

- name: Configure SSH to use System Crypto Policy
  ansible.builtin.lineinfile:
    dest: /etc/sysconfig/sshd
    state: absent
    regexp: (?i)^\s*CRYPTO_POLICY.*$
  when: '"kernel-core" in ansible_facts.packages'
  tags:
  - CCE-80939-2
  - DISA-STIG-RHEL-08-010287
  - NIST-800-53-AC-17(2)
  - NIST-800-53-AC-17(a)
  - NIST-800-53-CM-6(a)
  - NIST-800-53-MA-4(6)
  - NIST-800-53-SC-13
  - PCI-DSS-Req-2.2
  - PCI-DSSv4-2.2
  - PCI-DSSv4-2.2.7
  - configure_ssh_crypto_policy
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required