cis-ubuntu1604-v200-3-5-1-4

name	cis-ubuntu1604-v200-3-5-1-4
description	Ensure ufw loopback traffic is configured
category	cis-networking
version	2.0.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-16.04","firewall"]
cis_id	3.5.1.4
cis_benchmark	CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0
tech_stack	["ubuntu","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0 - Control 3.5.1.4

Profile

• Level: Level 1 - Server, Level 1 - Workstation
• Assessment Status: Automated

Description

Configure the loopback interface to accept traffic. Configure all other interfaces to deny traffic to the loopback network (127.0.0.0/8 for IPv4 and ::1/128 for IPv6).

Rationale

Loopback traffic is generated between processes on machine and is typically critical to operation of the system. The loopback interface is the only place that loopback network (127.0.0.0/8 for IPv4 and ::1/128 for IPv6) traffic should be seen, all other interfaces should ignore traffic on this network as an anti-spoofing measure.

Audit Procedure

Command Line

Run the following commands and verify output includes the listed rules in order:

ufw status verbose

Expected Result

To                         Action      From
--                         ------      ----
Anywhere on lo             ALLOW IN    Anywhere
Anywhere                   DENY IN     127.0.0.0/8
Anywhere (v6) on lo        ALLOW IN    Anywhere (v6)
Anywhere (v6)              DENY IN     ::1

Anywhere                   ALLOW OUT   Anywhere on lo
Anywhere (v6)              ALLOW OUT   Anywhere (v6) on lo

Remediation

Command Line

Run the following commands to implement the loopback rules:

ufw allow in on lo
ufw allow out on lo
ufw deny in from 127.0.0.0/8
ufw deny in from ::1

References

None

CIS Controls

Version 7

9.4 Apply Host-based Firewalls or Port Filtering - Apply host-based firewalls or port filtering tools on end systems, with a default-deny rule that drops all traffic except those services and ports that are explicitly allowed.