Cis Ubuntu2004 V300 3 3 3

---
name: cis-ubuntu2004-v300-3-3-3
description: "Ensure bogus icmp responses are ignored"
category: cis-networking
version: "3.0.0"
author: cyberstrike-official
tags: [cis, ubuntu, linux, ubuntu-20.04, kernel-parameter]
cis_id: "3.3.3"
cis_benchmark: "CIS Ubuntu Linux 20.04 LTS Benchmark v3.0.0"
tech_stack: [ubuntu, linux]
cwe_ids: []
chains_with: []
prerequisites: []
severity_boost: {}
---

# 3.3.3 Ensure bogus icmp responses are ignored (Automated)

## Profile

- Level 1 - Server
- Level 1 - Workstation

## Description

Setting `net.ipv4.icmp_ignore_bogus_error_responses` to 1 prevents the kernel from logging bogus responses (RFC-1122 non-compliant) from broadcast reframes, keeping file systems from filling up with useless log messages.

## Rationale

Some routers (and some attackers) will send responses that violate RFC-1122 and attempt to fill up a log file system with many useless error messages.

## Impact

None expected.

## Audit Procedure

### Command Line

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

- `net.ipv4.icmp_ignore_bogus_error_responses` is set to 1

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 If that file is superseded, the parameter is overridden by an incorrect setting later in that file, or in a canonically later file, that "correct" setting will be ignored both by the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 `net.ipv4.icmp_ignore_bogus_error_responses` set to 1.

## Remediation

### Command Line

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

- `net.ipv4.icmp_ignore_bogus_error_responses = 1`

Example:

```bash
# printf '%s\n' "net.ipv4.icmp_ignore_bogus_error_responses = 1" >> /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.icmp_ignore_bogus_error_responses=1
  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.icmp_ignore_bogus_error_responses = 1

## References

1. NIST SP 800-53 Rev. 5: CM-1, CM-2, CM-6, CM-7, IA-5

## 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    |