# CIS Ubuntu 14.04 LTS - 3.2.5 Ensure broadcast ICMP requests are ignored

> Verify that broadcast ICMP echo and timestamp requests are ignored to prevent Smurf attacks

- Skill: `cyberstrikeus/cis-ubuntu-14-04-lts-3-2-5-ensure-broadcast-icmp-requests-ar` (Agent Skill)
- Install (CLI): `npx skillmds@latest add cyberstrikeus/cis-ubuntu-14-04-lts-3-2-5-ensure-broadcast-icmp-requests-ar`
- Raw SKILL.md: https://api.skillmd.com/api/skills/cyberstrikeus/cis-ubuntu-14-04-lts-3-2-5-ensure-broadcast-icmp-requests-ar/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-ubuntu-14-04-lts-3-2-5-ensure-broadcast-icmp-requests-ar

---


# 3.2.5 Ensure broadcast ICMP requests are ignored (Scored)

## Profile Applicability

- Level 1 - Server
- Level 1 - Workstation

## 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 routable. If many hosts respond to the packets, the amount of traffic on the network could be significantly multiplied.

## Audit Procedure

Run the following commands and verify output matches:

```bash
sysctl net.ipv4.icmp_echo_ignore_broadcasts
# Expected: net.ipv4.icmp_echo_ignore_broadcasts = 1

grep "net\.ipv4\.icmp_echo_ignore_broadcasts" /etc/sysctl.conf /etc/sysctl.d/*
# Expected: net.ipv4.icmp_echo_ignore_broadcasts = 1
```

## Expected Result

```
net.ipv4.icmp_echo_ignore_broadcasts = 1
```

## Remediation

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

Not specified.

## References

- CIS Controls: 3 - Secure Configurations for Hardware and Software on Mobile Devices, Laptops, Workstations, and Servers
- CIS Controls: 11 - Secure Configurations for Network Devices such as Firewalls, Routers and switches

## Profile

- Level 1 - Server
- Level 1 - Workstation