# Cis GCP Cos 3.2.4

> Ensure suspicious packets are logged

- Skill: `cyberstrikeus/cis-gcp-cos-3-2-4` (Agent Skill)
- Install (CLI): `npx skillmds@latest add cyberstrikeus/cis-gcp-cos-3-2-4`
- Raw SKILL.md: https://api.skillmd.com/api/skills/cyberstrikeus/cis-gcp-cos-3-2-4/raw
- Safety review: PASS (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: DevOps & Infra
- Author: cyberstrikeus (https://skillmd.com/u/cyberstrikeus)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/cyberstrikeus/cis-gcp-cos-3-2-4

---


# 3.2.4 Ensure suspicious packets are logged (Automated)

## Description

When enabled, this feature logs packets with un-routable source addresses to the kernel log.

## Rationale

Enabling this feature and logging these packets allows an administrator to investigate the possibility that an attacker is sending spoofed packets to their system.

## Audit Procedure

Run the following commands and verify output matches:

```bash
# sysctl net.ipv4.conf.all.log_martians
net.ipv4.conf.all.log_martians = 1
# sysctl net.ipv4.conf.default.log_martians
net.ipv4.conf.default.log_martians = 1
```

## Expected Result

Both sysctl commands should return a value of `1`, confirming that suspicious (martian) packets are being logged.

## Remediation

Run the following commands to set the active kernel parameters:

```bash
# sysctl -w net.ipv4.conf.all.log_martians=1
# sysctl -w net.ipv4.conf.default.log_martians=1
# sysctl -w net.ipv4.route.flush=1
```

`/etc` is stateless on Container-Optimized OS. Therefore, `/etc` cannot be used to make these changes persistent across reboots. The steps mentioned above needs to be performed after every boot.

## CIS Controls

| Controls Version | Control                                                                                                                                                                                                                                                                                    | IG 1 | IG 2 | IG 3 |
| ---------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ---- | ---- | ---- |
| v8               | **8.2 Collect Audit Logs** - Collect audit logs. Ensure that logging, per the enterprise's audit log management process, has been enabled across enterprise assets.                                                                                                                        | X    | X    | X    |
| v8               | **8.5 Collect Detailed Audit Logs** - Configure detailed audit logging for enterprise assets containing sensitive data. Include event source, date, username, timestamp, source addresses, destination addresses, and other useful elements that could assist in a forensic investigation. |      | X    | X    |
| v7               | **6.2 Activate audit logging** - Ensure that local logging has been enabled on all systems and networking devices.                                                                                                                                                                         | X    | X    | X    |
| v7               | **6.3 Enable Detailed Logging** - Enable system logging to include detailed information such as an event source, date, user, timestamp, source addresses, destination addresses, and other useful elements.                                                                                |      | X    | X    |

## Profile

- Level 2 - Server