cis-ubuntu1804-v220-3-3-4

name	cis-ubuntu1804-v220-3-3-4
description	Ensure broadcast ICMP requests are ignored
category	cis-networking
version	2.2.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-18.04","networking","kernel-parameter"]
cis_id	3.3.4
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 3.3.4

Description

Setting net.ipv4.icmp_echo_ignore_broadcasts to 1 will cause the system to ignore all ICMP echo and timestamp requests to broadcast and multicast addresses.

Rationale

Accepting ICMP echo and timestamp requests with broadcast or multicast destinations for your network could be used to trick your host into starting (or participating) in a Smurf attack. A Smurf attack relies on an attacker sending large amounts of ICMP broadcast messages with a spoofed source address. All hosts receiving this message and responding would send echo-reply messages back to the spoofed address, which is probably not combatable. If many hosts respond to the packets, the amount of traffic on the network could be significantly multiplied.

Impact

None.

Audit Procedure

Command Line

Run the following command to verify broadcast ICMP requests are ignored:

sysctl net.ipv4.icmp_echo_ignore_broadcasts

grep -E '^\s*net\.ipv4\.icmp_echo_ignore_broadcasts\s*=\s*1\b' /etc/sysctl.conf /etc/sysctl.d/*.conf

Expected Result

net.ipv4.icmp_echo_ignore_broadcasts = 1

Remediation

Command Line

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

net.ipv4.icmp_echo_ignore_broadcasts = 1

Run the following commands to set the active kernel parameters:

sysctl -w net.ipv4.icmp_echo_ignore_broadcasts=1
sysctl -w net.ipv4.route.flush=1

Default Value

net.ipv4.icmp_echo_ignore_broadcasts = 1

References

1. NIST SP 800-53 Rev. 5: CM-7, SC-5
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