Cis Ubuntu1404 V210 3 2 2

---
name: "CIS Ubuntu 14.04 LTS - 3.2.2 Ensure ICMP redirects are not accepted"
description: "Verify that ICMP redirects are not accepted to prevent routing table manipulation"
category: "cis-os-hardening"
version: "2.1.0"
author: "cyberstrike-official"
tags:
  - cis
  - ubuntu
  - ubuntu-14.04
  - level-1
  - scored
  - network
cis_id: "3.2.2"
cis_benchmark: "CIS Ubuntu Linux 14.04 LTS Benchmark v2.1.0"
tech_stack:
  - ubuntu
  - linux
cwe_ids: []
chains_with: []
prerequisites: []
severity_boost: "medium"
---

# 3.2.2 Ensure ICMP redirects are not accepted (Scored)

## Profile Applicability

- Level 1 - Server
- Level 1 - Workstation

## Description

ICMP redirect messages are packets that convey routing information and tell your host (acting as a router) to send packets via an alternate path. It is a way of allowing an outside routing device to update your system routing tables. By setting `net.ipv4.conf.all.accept_redirects` to 0, the system will not accept any ICMP redirect messages, and therefore, won't allow outsiders to update the system's routing tables.

## Rationale

Attackers could use bogus ICMP redirect messages to maliciously alter the system routing tables and get them to send packets to incorrect networks and allow your system packets to be captured.

## Audit Procedure

Run the following commands and verify output matches:

```bash
sysctl net.ipv4.conf.all.accept_redirects
# Expected: net.ipv4.conf.all.accept_redirects = 0

sysctl net.ipv4.conf.default.accept_redirects
# Expected: net.ipv4.conf.default.accept_redirects = 0

grep "net\.ipv4\.conf\.all\.accept_redirects" /etc/sysctl.conf /etc/sysctl.d/*
# Expected: net.ipv4.conf.all.accept_redirects= 0

grep "net\.ipv4\.conf\.default\.accept_redirects" /etc/sysctl.conf /etc/sysctl.d/*
# Expected: net.ipv4.conf.default.accept_redirects= 0
```

## Expected Result

```
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.default.accept_redirects = 0
```

## Remediation

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

```
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.default.accept_redirects = 0
```

Run the following commands to set the active kernel parameters:

```bash
sysctl -w net.ipv4.conf.all.accept_redirects=0
sysctl -w net.ipv4.conf.default.accept_redirects=0
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