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CIS Ubuntu 14.04 LTS - 3.3.2 Ensure IPv6 redirects are not accepted

DevOps & Security
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Verify that IPv6 ICMP redirects are not accepted to prevent routing to compromised machines

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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-v210-3-3-2/SKILL.md

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3.3.2 Ensure IPv6 redirects are not accepted (Not Scored)

Profile Applicability

  • Level 1 - Server
  • Level 1 - Workstation

Description

This setting prevents the system from accepting ICMP redirects. ICMP redirects tell the system about alternate routes for sending traffic.

Rationale

It is recommended that systems not accept ICMP redirects as they could be tricked into routing traffic to compromised machines. Setting hard routes within the system (usually a single default route to a trusted router) protects the system from bad routes.

Audit Procedure

Run the following commands and verify output matches:

sysctl net.ipv6.conf.all.accept_redirects
# Expected: net.ipv6.conf.all.accept_redirect = 0

sysctl net.ipv6.conf.default.accept_redirects
# Expected: net.ipv6.conf.default.accept_redirect = 0

grep "net\.ipv6\.conf\.all\.accept_redirect" /etc/sysctl.conf /etc/sysctl.d/*
# Expected: net.ipv6.conf.all.accept_redirect = 0

grep "net\.ipv6\.conf\.default\.accept_redirect" /etc/sysctl.conf /etc/sysctl.d/*
# Expected: net.ipv6.conf.default.accept_redirect = 0

Expected Result

net.ipv6.conf.all.accept_redirects = 0
net.ipv6.conf.default.accept_redirects = 0

Remediation

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

net.ipv6.conf.all.accept_redirects = 0
net.ipv6.conf.default.accept_redirects = 0

Run the following commands to set the active kernel parameters:

sysctl -w net.ipv6.conf.all.accept_redirects=0
sysctl -w net.ipv6.conf.default.accept_redirects=0
sysctl -w net.ipv6.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