cis-ubuntu1804-v220-1-8-5

name	cis-ubuntu1804-v220-1-8-5
description	Ensure GDM screen locks cannot be overridden
category	cis-networking
version	2.2.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-18.04","gdm","gnome","screen-lock","lockdown","dconf"]
cis_id	1.8.5
cis_benchmark	CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0
tech_stack	["ubuntu","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

1.8.5 Ensure GDM screen locks cannot be overridden (Automated)

Profile Applicability

• Level 1 - Server
• Level 1 - Workstation

Description

GNOME Desktop Manager can make the screen lock automatically whenever the user is idle for some amount of time.

By using the lockdown mode in dconf, you can prevent users from changing specific settings.

To lock down a dconf key or subpath, create a locks subdirectory in the keyfile directory. The files inside this directory contain a list of keys or subpaths to lock. Just as with the keyfiles, you may add any number of files to this directory.

Example Lock File:

# Lock desktop screensaver settings
/org/gnome/desktop/session/idle-delay
/org/gnome/desktop/screensaver/lock-delay

Rationale

Setting a lock-out value reduces the window of opportunity for unauthorized user access to another user's session that has been left unattended.

Without locking down the system settings, user settings take precedence over the system settings.

Audit Procedure

Command Line

Run the following script to verify that the screen lock cannot be overridden:

#!/usr/bin/env bash

{
    # Check if GNOME Desktop Manager is installed. If package isn't installed, recommendation is Not Applicable\n
    # determine system's package manager
    l_pkgoutput=""
    if command -v dpkg-query > /dev/null 2>&1; then
        l_pq="dpkg-query -s"
    elif command -v rpm > /dev/null 2>&1; then
        l_pq="rpm -q"
    fi
    # Check if GDM is installed
    l_pcl="gdm gdm3" # Space separated list of packages to check
    for l_pn in $l_pcl; do
        $l_pq "$l_pn" > /dev/null 2>&1 && l_pkgoutput="$l_pkgoutput\n - Package: \"\" exists on the system\n - checking configuration"
    
    
     [ -n  ]; 
        l_output= l_output2=
        
        l_kfd=. 
        l_kfd2=. 
         [ -d  ];  
             grep -Prilq  ; 
                l_output=
            
                l_output2=
            
        
            l_output2=
        
         [ -d  ];  
             grep -Prilq  ; 
                l_output=
            
                l_output2=
            
        
            l_output2=
        
    
        l_output=
    
    
    [ -n  ] &&  -e 
     [ -z  ]; 
         -e 
    
         -e 
        [ -n  ] &&  -e 
    
}