# Cis Ubuntu1604 V200 3 3 3

> Ensure secure ICMP redirects are not accepted

- Skill: `cyberstrikeus/cis-ubuntu1604-v200-3-3-3` (Agent Skill)
- Install (CLI): `npx skillmds@latest add cyberstrikeus/cis-ubuntu1604-v200-3-3-3`
- Raw SKILL.md: https://api.skillmd.com/api/skills/cyberstrikeus/cis-ubuntu1604-v200-3-3-3/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-ubuntu1604-v200-3-3-3

---


# CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0 - Control 3.3.3

## Description

Secure ICMP redirects are the same as ICMP redirects, except they come from gateways listed on the default gateway list. It is assumed that these gateways are known to your system, and that they are likely to be secure.

## Rationale

It is still possible for even known gateways to be compromised. Setting `net.ipv4.conf.all.secure_redirects` to 0 protects the system from routing table updates by possibly compromised known gateways.

## Impact

None.

## Audit Procedure

### Command Line

Run the following commands and verify output matches:

```bash
sysctl net.ipv4.conf.all.secure_redirects
```

```bash
sysctl net.ipv4.conf.default.secure_redirects
```

```bash
grep "net\.ipv4\.conf\.all\.secure_redirects" /etc/sysctl.conf /etc/sysctl.d/*
```

```bash
grep "net\.ipv4\.conf\.default\.secure_redirects" /etc/sysctl.conf /etc/sysctl.d/*
```

## Expected Result

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

And the grep commands should return:

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

## Remediation

### Command Line

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

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

Run the following commands to set the active kernel parameters:

```bash
sysctl -w net.ipv4.conf.all.secure_redirects=0
sysctl -w net.ipv4.conf.default.secure_redirects=0
sysctl -w net.ipv4.route.flush=1
```

## Default Value

secure_redirects is enabled (set to 1) by default.

## References

1. CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0

## CIS Controls

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