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cis-ubuntu1604-v200-3-2-1

DevOps & Security
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Ensure packet redirect sending is disabled

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Source SKILL.md: https://github.com/CyberStrikeus/CyberStrike/blob/HEAD/.cyberstrike/skill/CIS_benchmarks/Operating_Systems/Ubuntu/CIS_Ubuntu_Linux_16.04_LTS_Benchmark_v2.0.0/cis-ubuntu1604-v200-3-2-1/SKILL.md

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CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0 - Control 3.2.1

Description

ICMP Redirects are used to send routing information to other hosts. As a host itself does not act as a router (in a host only configuration), there is no need to send redirects.

Rationale

An attacker could use a compromised host to send invalid ICMP redirects to other router devices in an attempt to corrupt routing and have users access a system set up by the attacker as opposed to a valid system.

Impact

None.

Audit Procedure

Command Line

Run the following commands and verify output matches:

sysctl net.ipv4.conf.all.send_redirects

sysctl net.ipv4.conf.default.send_redirects

grep -E "^\s*net\.ipv4\.conf\.all\.send_redirects" /etc/sysctl.conf /etc/sysctl.d/*

grep -E "^\s*net\.ipv4\.conf\.default\.send_redirects" /etc/sysctl.conf /etc/sysctl.d/*

Expected Result

net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.default.send_redirects = 0

And the grep commands should return:

net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.default.send_redirects= 0

Remediation

Command Line

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

net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.default.send_redirects = 0

Run the following commands to set the active kernel parameters:

sysctl -w net.ipv4.conf.all.send_redirects=0
sysctl -w net.ipv4.conf.default.send_redirects=0
sysctl -w net.ipv4.route.flush=1

Default Value

send_redirects is enabled (set to 1) by default.

References

  1. CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0

CIS Controls

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