cis-gcp-cos-3-2-3

name	cis-gcp-cos-3.2.3
description	Ensure secure ICMP redirects are not accepted
category	cis-gcp-cos
version	1.2.0
author	cyberstrike-official
tags	["cis","gcp","container-optimized-os","network","sysctl","icmp","routing"]
cis_id	3.2.3
cis_benchmark	CIS Google Container-Optimized OS Benchmark v1.2.0
tech_stack	["gcp","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

3.2.3 Ensure secure ICMP redirects are not accepted (Automated)

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.

Audit Procedure

Run the following commands and verify output matches:

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

Expected Result

Both sysctl commands should return a value of 0, confirming that secure ICMP redirects are not accepted.

Remediation

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

/etc is stateless on Container-Optimized OS. Therefore, /etc cannot be used to make these changes persistent across reboots. The steps mentioned above needs to be performed after every boot.

CIS Controls

Controls Version	Control	IG 1	IG 2	IG 3
v8	12.2 Establish and Maintain a Secure Network Architecture - Establish and maintain a secure network architecture. A secure network architecture must address segmentation, least privilege, and availability, at a minimum.		X	X
v7	5.1 Establish Secure Configurations - Maintain documented, standard security configuration standards for all authorized operating systems and software.	X	X	X

Profile

• Level 2 - Server