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cis-ubuntu1804-v220-3-3-3

DevOps & Security
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Ensure bogus ICMP responses are ignored

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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-v220-3-3-3/SKILL.md

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CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0 - Control 3.3.3

Description

Setting 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.

Audit Procedure

Command Line

Run the following command to verify bogus ICMP responses are ignored:

sysctl net.ipv4.icmp_ignore_bogus_error_responses

grep -E '^\s*net\.ipv4\.icmp_ignore_bogus_error_responses\s*=\s*1\b' /etc/sysctl.conf /etc/sysctl.d/*.conf

Expected Result

net.ipv4.icmp_ignore_bogus_error_responses = 1

Remediation

Command Line

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

net.ipv4.icmp_ignore_bogus_error_responses = 1

Run the following commands to set the active kernel parameters:

sysctl -w net.ipv4.icmp_ignore_bogus_error_responses=1
sysctl -w net.ipv4.route.flush=1

Default Value

net.ipv4.icmp_ignore_bogus_error_responses = 1

References

  1. NIST SP 800-53 Rev. 5: CM-7, SC-5
  2. CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0

CIS Controls

Version 8

4.1 Establish and Maintain a Secure Configuration Process - Establish and maintain a secure configuration process for enterprise assets.

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