cis-ubuntu2004-v300-3-3-11

DevOps & Security

Ensure ipv6 router advertisements are not accepted

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3.3.11 Ensure ipv6 router advertisements are not accepted (Automated)

Profile

Level 1 - Server
Level 1 - Workstation

Description

Routers periodically multicast Router Advertisement messages to announce their availability and convey information to neighboring nodes that enable them to be automatically configured on the network.

net.ipv6.conf.all.accept_ra and net.ipv6.conf.default.accept_ra determine the systems ability to accept these advertisements.

Rationale

It is recommended that systems do not accept router advertisements 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. Setting net.ipv6.conf.all.accept_ra and net.ipv6.conf.default.accept_ra to 0 disables the system's ability to accept IPv6 router advertisements.

Impact

None expected.

Audit Procedure

Command Line

Run the following script to verify the following kernel parameters are set in the running configuration and correctly loaded from a kernel parameter configuration file:

net.ipv6.conf.all.accept_ra is set to 0
net.ipv6.conf.default.accept_ra is set to 0

Note:

kernel parameters are loaded by file and parameter order precedence. The following script observes this precedence as part of the auditing procedure. The parameters being checked may be set correctly in a file. If that file is superseded, the parameter is overridden by an incorrect setting later in that file, or in a canonically later file, that "correct" setting will be ignored both by the script and by the system during a normal kernel parameter load sequence.
IPv6 kernel parameters only apply to systems where IPv6 is enabled

Expected Result

Audit Result: ** PASS ** with both net.ipv6.conf.all.accept_ra and net.ipv6.conf.default.accept_ra set to 0 (or IPv6 disabled on the system).

Remediation

Command Line

IF - IPv6 is enabled on the system: Set the following parameters in /etc/sysctl.conf or a file in /etc/sysctl.d/ ending in .conf:
net.ipv6.conf.all.accept_ra = 0
net.ipv6.conf.default.accept_ra = 0

Example:

# printf '%s\n' "net.ipv6.conf.all.accept_ra = 0" "net.ipv6.conf.default.accept_ra = 0" >> /etc/sysctl.d/60-
netipv6_sysctl.conf

Run the following script to set the active kernel parameters:

#!/usr/bin/env bash

{
  sysctl -w net.ipv6.conf.all.accept_ra=0
  sysctl -w net.ipv6.conf.default.accept_ra=0
  sysctl -w net.ipv6.route.flush=1
}

Note: If these settings appear in a canonically later file, or later in the same file, these settings will be overwritten.

Default Value

net.ipv6.conf.all.accept_ra = 1

net.ipv6.conf.default.accept_ra = 1

References

NIST SP 800-53 :: CM-6 b
NIST SP 800-53A :: CM-6.1 (iv)
RHEL 8 STIG Vul ID: V-230541
RHEL 8 STIG Rule ID: SV-230541r858812
RHEL 8 STIG Vul ID: V-230542
RHEL 8 STIG Rule ID: SV-230542r858814

CIS Controls

Controls Version	Control	IG 1	IG 2	IG 3
v8	4.8 Uninstall or Disable Unnecessary Services on Enterprise Assets and Software		x	x
v7	9.2 Ensure Only Approved Ports, Protocols and Services Are Running		x	x