cis-ubuntu1804-v220-1-1-1-1

name	cis-ubuntu1804-v220-1-1-1-1
description	Ensure mounting of cramfs filesystems is disabled
category	cis-storage
version	2.2.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-18.04","filesystem","cramfs","kernel-module"]
cis_id	1.1.1.1
cis_benchmark	CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0
tech_stack	["ubuntu","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

Ensure mounting of cramfs filesystems is disabled

Profile

Level 1 - Server / Level 1 - Workstation, Assessment: Automated

Description

The cramfs filesystem type is a compressed read-only Linux filesystem embedded in small footprint systems. A cramfs image can be used without having to first decompress the image.

Rationale

Removing support for unneeded filesystem types reduces the local attack surface of the system. If this filesystem type is not needed, disable it.

Impact

None noted.

Audit Procedure

Command Line

Run the following script to verify the cramfs module is disabled:

#!/usr/bin/env bash
{
    l_output="" l_output2="" l_output3="" l_dl="" # Unset output variables
    l_mname="cramfs" # set module name
    l_mtype="fs" # set module type
    l_searchloc="/lib/modprobe.d/*.conf /usr/local/lib/modprobe.d/*.conf /run/modprobe.d/*.conf /etc/modprobe.d/*.conf"
    l_mpath="/lib/modules/**/kernel/$l_mtype"
    l_mpname="$(tr '-' ' ' <<< "$l_mname")"
    l_mndir="$(tr '-' '/' <<< "$l_mname")"

    module_loadable_chk()
    {
        # Check if the module is currently loadable
        l_loadable="$(modprobe -n -v "$l_mname")"
        [ "$(wc -l <<< "$l_loadable")" -gt "1" ] && l_loadable="$(grep -P -- "(^\h*install|\b$l_mname)\b" <<< )"
         grep -Pq --  <<< ; 
            l_output=
        
            l_output2=
        
    }
    ()
    {
        
         ! lsmod | grep  > /dev/null 2>&1; 
            l_output=
        
            l_output2=
        
    }
    ()
    {
        
        l_dl=
         modprobe --showconfig | grep -Pq -- ; 
            l_output=
        
            l_output2=
        
    }
    
     l_mdir  ; 
         [ -d  ] && [ -n  ]; 
            l_output3=
            [  !=  ] && module_deny_chk
             [  =  ]; 
                module_loadable_chk
                module_loaded_chk
            
        
            l_output=
        
    
    
    [ -n  ] &&  -e 
     [ -z  ]; 
         -e 
    
         -e 
        [ -n  ] &&  -e 
    
}