cis-ubuntu1804-v220-3-3-6

name	cis-ubuntu1804-v220-3-3-6
description	Ensure secure ICMP redirects are not accepted
category	cis-networking
version	2.2.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-18.04","networking","kernel-parameter"]
cis_id	3.3.6
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 3.3.6

Description

Secure ICMP redirects are the same as ICMP redirects, except they come from gateways listed in the default gateway list. It is assumed that these gateways are known to be legitimate, so the risk is lower. However, it is still possible for even known gateways to be compromised.

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 to verify secure ICMP redirects are not accepted:

sysctl net.ipv4.conf.all.secure_redirects
sysctl net.ipv4.conf.default.secure_redirects

grep -E '^\s*net\.ipv4\.conf\.(all|default)\.secure_redirects\s*=\s*0\b' /etc/sysctl.conf /etc/sysctl.d/*.conf

Expected Result

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

net.ipv4.conf.all.secure_redirects = 1, net.ipv4.conf.default.secure_redirects = 1

References

1. NIST SP 800-53 Rev. 5: CM-7, SC-5, SC-7
2. CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0

CIS Controls

Version 8

4.1 Establish and Maintain a Secure Configuration Process - Establish and maintain a secure configuration process for enterprise assets.

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