# Cis Ubuntu1804 V220 3 3 4

> Ensure broadcast ICMP requests are ignored

- Skill: `cyberstrikeus/cis-ubuntu1804-v220-3-3-4` (Agent Skill)
- Install (CLI): `npx skillmds@latest add cyberstrikeus/cis-ubuntu1804-v220-3-3-4`
- Raw SKILL.md: https://api.skillmd.com/api/skills/cyberstrikeus/cis-ubuntu1804-v220-3-3-4/raw
- Safety review: PASS (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: cyberstrikeus (https://skillmd.com/u/cyberstrikeus)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/cyberstrikeus/cis-ubuntu1804-v220-3-3-4

---


# 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:

```bash
sysctl net.ipv4.icmp_echo_ignore_broadcasts
```

```bash
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:

```bash
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