Puppet Class: cis_security_hardening::rules::sshd_macs

Defined in:
manifests/rules/sshd_macs.pp

Summary

Ensure only approved MAC algorithms are used

Overview

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.

Examples:

class { 'cis_security_hardening::rules::sshd_macs':
    enforce => true,
    macs => ['a','b'],
}

Parameters:

  • enforce (Boolean) (defaults to: false) —

    Enforce the rule

  • macs (Array) (defaults to: []) —

    MAC algorithms to add to config



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# File 'manifests/rules/sshd_macs.pp', line 25

class cis_security_hardening::rules::sshd_macs (
  Boolean $enforce  = false,
  Array $macs       = [],
) {
  if $enforce {
    if (!empty($macs)) {
      $path = ($facts['os']['name'] == 'SLES' and $facts['os']['release']['major'] == '12') ? {
        true    => '/usr/etc/ssh/sshd_config',
        default => '/etc/ssh/sshd_config',
      }
      $maclist = $macs.join(',')
      file_line { 'sshd-macs':
        ensure => present,
        path   => $path,
        line   => "MACs ${maclist}",
        match  => '^#?MACs.*',
        notify => Exec['reload-sshd'],
      }
    }
  }
}