Cis Ubuntu1404 V210 3 2 5

---
name: "CIS Ubuntu 14.04 LTS - 3.2.5 Ensure broadcast ICMP requests are ignored"
description: "Verify that broadcast ICMP echo and timestamp requests are ignored to prevent Smurf attacks"
category: "cis-os-hardening"
version: "2.1.0"
author: "cyberstrike-official"
tags:
  - cis
  - ubuntu
  - ubuntu-14.04
  - level-1
  - scored
  - network
cis_id: "3.2.5"
cis_benchmark: "CIS Ubuntu Linux 14.04 LTS Benchmark v2.1.0"
tech_stack:
  - ubuntu
  - linux
cwe_ids: []
chains_with: []
prerequisites: []
severity_boost: "medium"
---

# 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