cis-ubuntu2004-v300-5-1-2

name	cis-ubuntu2004-v300-5-1-2
description	Ensure access to SSH private host key files is configured
category	cis-networking
version	3.0.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-20.04","ssh"]
cis_id	5.1.2
cis_benchmark	CIS Ubuntu Linux 20.04 LTS Benchmark v3.0.0
tech_stack	["ubuntu","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

Ensure access to SSH private host key files is configured (Automated)

Profile Applicability

• Level 1 - Server
• Level 1 - Workstation

Description

An SSH private key is one of two files used in SSH public key authentication. In this authentication method, the possession of the private key is proof of identity. Only a private key that corresponds to a public key will be able to authenticate successfully. The private keys need to be stored and handled carefully, and no copies of the private key should be distributed.

Rationale

If an unauthorized user obtains the private SSH host key file, the host could be impersonated

Audit Procedure

Command Line

Run the following script to verify SSH private host key files are owned by the root user and either:

• owned by the group root and mode 0600 or more restrictive

• OR -

• owned by the group designated to own openSSH private keys and mode 0640 or more restrictive

#!/usr/bin/env bash

{
  a_output=(); a_output2=()
  l_ssh_group_name="$(awk -F: '($1 ~ /^(ssh_keys|_?ssh)$/) {print $1}' /etc/group)"
  f_file_chk()
  {
    while IFS=: read -r l_file_mode l_file_owner l_file_group; do
      a_out2=()
      [ "$l_file_group" = "$l_ssh_group_name" ] && l_pmask="0137" || l_pmask="0177"
      l_maxperm="$( printf '%o' $(( 0777 & ~$l_pmask )) )"
      if [ $(( $l_file_mode & $l_pmask )) -gt 0 ]; then
        a_out2+=("      Mode: \"$l_file_mode\" should be mode: \"$l_maxperm\" or more restrictive")
      fi
      if [ "" !=  ]; 
        a_out2+=()
      
       [[ !  =~ (|root) ]]; 
        a_out2+=()
      
       [  -gt  ]; 
        a_output2+=( )
      
        a_output+=( \
         )
      
     < <( -Lc  )
  }
   IFS=  -r -d $ l_file; 
     ssh-keygen -lf &>/dev/null ; 
      file  | grep -Piq --  && f_file_chk
    
   < <(find -L /etc/ssh -xdev - f -print0 2>/dev/null)
   [  -le 0 ]; 
          
  
          
    [  -gt 0 ] &&      
  
}