cis-ubuntu1604-v200-3-3-3

name	cis-ubuntu1604-v200-3-3-3
description	Ensure secure ICMP redirects are not accepted
category	cis-networking
version	2.0.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-16.04","networking"]
cis_id	3.3.3
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 3.3.3

Description

Secure ICMP redirects are the same as ICMP redirects, except they come from gateways listed on the default gateway list. It is assumed that these gateways are known to your system, and that they are likely to be secure.

Rationale

It is still possible for even known gateways to be compromised. Setting net.ipv4.conf.all.secure_redirects to 0 protects the system from routing table updates by possibly compromised known gateways.

Impact

None.

Audit Procedure

Command Line

Run the following commands and verify output matches:

sysctl net.ipv4.conf.all.secure_redirects

sysctl net.ipv4.conf.default.secure_redirects

grep "net\.ipv4\.conf\.all\.secure_redirects" /etc/sysctl.conf /etc/sysctl.d/*

grep "net\.ipv4\.conf\.default\.secure_redirects" /etc/sysctl.conf /etc/sysctl.d/*

Expected Result

net.ipv4.conf.all.secure_redirects = 0
net.ipv4.conf.default.secure_redirects = 0

And the grep commands should return:

net.ipv4.conf.all.secure_redirects= 0
net.ipv4.conf.default.secure_redirects= 0

Remediation

Command Line

Set the following parameters in /etc/sysctl.conf or a /etc/sysctl.d/* file:

net.ipv4.conf.all.secure_redirects = 0
net.ipv4.conf.default.secure_redirects = 0

Run the following commands to set the active kernel parameters:

sysctl -w net.ipv4.conf.all.secure_redirects=0
sysctl -w net.ipv4.conf.default.secure_redirects=0
sysctl -w net.ipv4.route.flush=1

Default Value

secure_redirects is enabled (set to 1) by default.

References

1. CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0

CIS Controls

Version 7

5.1 Establish Secure Configurations - Maintain documented, standard security configuration standards for all authorized operating systems and software.

Profile Applicability

• Level 1 - Server
• Level 1 - Workstation

Assessment Status

Automated