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cis-ubuntu1804-v220-3-3-9

DevOps & Security
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Ensure suspicious packets are logged

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How to use this skill

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Prompt to paste
I want to install this Agent Skill for this project in Codex.

Source SKILL.md: https://github.com/CyberStrikeus/CyberStrike/blob/HEAD/.cyberstrike/skill/CIS_benchmarks/Operating_Systems/Ubuntu/CIS_Ubuntu_Linux_18.04_LTS_Benchmark_v2.2.0/cis-ubuntu1804-v220-3-3-9/SKILL.md

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Copying this prompt does not install or run the skill. Review third-party files before use. Codex skill guide

CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0 - Control 3.3.9

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.

Impact

None.

Audit Procedure

Command Line

Run the following commands to verify suspicious packets are logged:

sysctl net.ipv4.conf.all.log_martians
sysctl net.ipv4.conf.default.log_martians

grep -E '^\s*net\.ipv4\.conf\.(all|default)\.log_martians\s*=\s*1\b' /etc/sysctl.conf /etc/sysctl.d/*.conf

Expected Result

net.ipv4.conf.all.log_martians = 1
net.ipv4.conf.default.log_martians = 1

Remediation

Command Line

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

net.ipv4.conf.all.log_martians = 1
net.ipv4.conf.default.log_martians = 1

Run the following commands to set the active kernel parameters:

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

Default Value

net.ipv4.conf.all.log_martians = 0, net.ipv4.conf.default.log_martians = 0

References

  1. NIST SP 800-53 Rev. 5: AU-3, SC-5
  2. CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0

CIS Controls

Version 8

8.5 Collect Detailed Audit Logs - Configure detailed audit logging for enterprise assets containing sensitive data.

Version 7

6.2 Activate Audit Logging - Ensure that local logging has been enabled on all systems and networking devices.

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.

Profile Applicability

  • Level 1 - Server
  • Level 1 - Workstation

Assessment Status

Automated