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CIS Ubuntu 14.04 LTS - 3.2.6 Ensure bogus ICMP responses are ignored

DevOps & Security
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Verify that bogus ICMP error responses are ignored to prevent log file pollution

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Source SKILL.md: https://github.com/CyberStrikeus/CyberStrike/blob/HEAD/.cyberstrike/skill/CIS_benchmarks/Operating_Systems/Ubuntu/CIS_Ubuntu_Linux_14.04_LTS_Benchmark_v2.1.0/cis-ubuntu1404-v210-3-2-6/SKILL.md

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3.2.6 Ensure bogus ICMP responses are ignored (Scored)

Profile Applicability

  • Level 1 - Server
  • Level 1 - Workstation

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.

Audit Procedure

Run the following commands and verify output matches:

sysctl net.ipv4.icmp_ignore_bogus_error_responses
# Expected: net.ipv4.icmp_ignore_bogus_error_responses = 1

grep "net\.ipv4\.icmp_ignore_bogus_error_responses" /etc/sysctl.conf /etc/sysctl.d/*
# Expected: net.ipv4.icmp_ignore_bogus_error_responses = 1

Expected Result

net.ipv4.icmp_ignore_bogus_error_responses = 1

Remediation

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

Not specified.

References

  • CIS Controls: 3 - Secure Configurations for Hardware and Software on Mobile Devices, Laptops, Workstations, and Servers
  • CIS Controls: 11 - Secure Configurations for Network Devices such as Firewalls, Routers and switches

Profile

  • Level 1 - Server
  • Level 1 - Workstation