cis-ubuntu1804-v220-3-3-1

name	cis-ubuntu1804-v220-3-3-1
description	Ensure ip forwarding is disabled
category	cis-networking
version	2.2.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-18.04","networking","kernel-parameter"]
cis_id	3.3.1
cis_benchmark	CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0
tech_stack	["ubuntu","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0 - Control 3.3.1

Description

The net.ipv4.ip_forward and net.ipv6.conf.all.forwarding flags are used to tell the system whether it can forward packets or not.

Rationale

Setting the flags to 0 ensures that a system with multiple interfaces (for example, a hard proxy), will never be able to forward packets, and therefore, never serve as a router.

Impact

None.

Audit Procedure

Command Line

Run the following script to verify IP forwarding is disabled:

#!/usr/bin/bash
{
  l_output="" l_output2=""
  a_parlist=("net.ipv4.ip_forward=0" "net.ipv6.conf.all.forwarding=0")
  l_ufwscf="$([ -f /etc/default/ufw ] && awk -F= '/^\s*IPT_SYSCTL=/ {print $2}' /etc/default/ufw)"

  kernel_parameter_chk() {
    l_krp="$(sysctl "$l_kpname" | awk -F= '{print $2}' | xargs)"
    if [ "$l_krp" = "$l_kpvalue" ]; then
      l_output="$l_output\n - \"$l_kpname\" is correctly set to \"$l_krp\" in the running configuration"
    else
      l_output2="$l_output2\n - \"$l_kpname\" is incorrectly set to \"$l_krp\" in the running configuration and should have a value of: \"$l_kpvalue\""
    fi
  }

  for l_kpe in "${a_parlist[@]}"; do
    l_kpname="$(awk -F= '{print $1}' <<< )"
    l_kpvalue=
    kernel_parameter_chk
  

   [ -z  ]; 
     -e 
  
     -e 
    [ -n  ] &&  -e 
  
}