Cis Ubuntu2004 V300 3 3 2

---
name: cis-ubuntu2004-v300-3-3-2
description: "Ensure packet redirect sending is disabled"
category: cis-networking
version: "3.0.0"
author: cyberstrike-official
tags: [cis, ubuntu, linux, ubuntu-20.04, kernel-parameter]
cis_id: "3.3.2"
cis_benchmark: "CIS Ubuntu Linux 20.04 LTS Benchmark v3.0.0"
tech_stack: [ubuntu, linux]
cwe_ids: []
chains_with: []
prerequisites: []
severity_boost: {}
---

# 3.3.2 Ensure packet redirect sending is disabled (Automated)

## Profile

- Level 1 - Server
- Level 1 - Workstation

## Description

ICMP Redirects are used to send routing information to other hosts. As a host itself does not act as a router (in a host only configuration), there is no need to send redirects.

## Rationale

An attacker could use a compromised host to send invalid ICMP redirects to other router devices in an attempt to corrupt routing and have users access a system set up by the attacker as opposed to a valid system.

## Impact

IP forwarding is required on systems configured to act as a router. If these parameters are disabled, the system will not be able to perform as a router.

## Audit Procedure

### Command Line

Run the following script to verify the following kernel parameters are set in the running configuration and correctly loaded from a kernel parameter configuration file:

- `net.ipv4.conf.all.send_redirects` is set to 0
- `net.ipv4.conf.default.send_redirects` is set to 0

Note: kernel parameters are loaded by file and parameter order precedence. The following script observes this precedence as part of the auditing procedure. The parameters being checked may be set correctly in a file. If that file is superseded, the parameter is overridden by an incorrect setting later in that file, or in a canonically later file, that "correct" setting will be ignored both by the script and by the system during a normal kernel parameter load sequence.

## Expected Result

Audit Result: ** PASS ** with both `net.ipv4.conf.all.send_redirects` and `net.ipv4.conf.default.send_redirects` set to 0.

## Remediation

### Command Line

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

- `net.ipv4.conf.all.send_redirects = 0`
- `net.ipv4.conf.default.send_redirects = 0`

Example:

```bash
# printf '%s\n' "net.ipv4.conf.all.send_redirects = 0" "net.ipv4.conf.default.send_redirects = 0" >>
/etc/sysctl.d/60-netipv4_sysctl.conf
```

Run the following script to set the active kernel parameters:

```bash
#!/usr/bin/env bash

{
  sysctl -w net.ipv4.conf.all.send_redirects=0
  sysctl -w net.ipv4.conf.default.send_redirects=0
  sysctl -w net.ipv4.route.flush=1
}
```

Note: If these settings appear in a canonically later file, or later in the same file, these settings will be overwritten.

## Default Value

net.ipv4.conf.all.send_redirects = 1

net.ipv4.conf.default.send_redirects = 1

## References

1. NIST SP 800-53 :: CM-6 b
2. NIST SP 800-53A :: CM-6.1 (iv)
3. RHEL 8 STIG GROUP ID: V-230536
4. RHEL 8 STIG RULE ID: SV-230536r858795
5. RHEL 8 STIG GROUP ID: V-230543
6. RHEL 8 STIG RULE ID: SV-230543r858816

## CIS Controls

| Controls Version | Control                                                                         | IG 1 | IG 2 | IG 3 |
| ---------------- | ------------------------------------------------------------------------------- | ---- | ---- | ---- |
| v8               | 4.8 Uninstall or Disable Unnecessary Services on Enterprise Assets and Software |      | x    | x    |
| v7               | 9.2 Ensure Only Approved Ports, Protocols and Services Are Running              |      | x    | x    |