cyberstrikeus CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0 - Control 3.3.9
Description
This setting disables the system's ability to accept IPv6 router 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.
Impact
None.
Audit Procedure
Command Line
IF IPv6 is enabled:
Run the following commands and verify output matches:
sysctl net.ipv6.conf.all.accept_ra
sysctl net.ipv6.conf.default.accept_ra
grep "net\.ipv6\.conf\.all\.accept_ra" /etc/sysctl.conf /etc/sysctl.d/*
grep "net\.ipv6\.conf\.default\.accept_ra" /etc/sysctl.conf /etc/sysctl.d/*
OR verify IPv6 is disabled:
Run the following script. Output will confirm if IPv6 is disabled on the system.
#!/usr/bin/bash
output=""
grubfile="$(find -L /boot -name 'grub.cfg' -type f)"
[ -f "$grubfile" ] && ! grep "^\s*linux" "$grubfile" | grep -vq ipv6.disable=1 && output="ipv6 disabled in grub config"
grep -Eqs "^\s*net\.ipv6\.conf\.all\.disable_ipv6\s*=\s*1\b" /etc/sysctl.conf /etc/sysctl.d/*.conf /usr/lib/sysctl.d/*.conf /run/sysctl.d/*.conf && grep -Eqs "^\s*net\.ipv6\.conf\.default\.disable_ipv6\s*=\s*1\b" /etc/sysctl.conf /etc/sysctl.d/*.conf /usr/lib/sysctl.d/*.conf /run/sysctl.d/*.conf && sysctl net.ipv6.conf.all.disable_ipv6 | grep -Eq "^\s*net\.ipv6\.conf\.all\.disable_ipv6\s*=\s*1\b" && sysctl net.ipv6.conf.default.disable_ipv6 | grep -Eq "^\s*net\.ipv6\.conf\.default\.disable_ipv6\s*=\s*1\b" && output="ipv6 disabled in sysctl config"
[ -n "$output" ] && echo -e "\n$output" || echo -e "\n*** IPv6 is enabled on the system ***"
Expected Result
If IPv6 is enabled:
net.ipv6.conf.all.accept_ra = 0
net.ipv6.conf.default.accept_ra = 0
And the grep commands should return:
net.ipv6.conf.all.accept_ra = 0
net.ipv6.conf.default.accept_ra = 0
Remediation
Command Line
IF IPv6 is enabled:
Set the following parameters in /etc/sysctl.conf or a /etc/sysctl.d/* file:
net.ipv6.conf.all.accept_ra = 0
net.ipv6.conf.default.accept_ra = 0
Run the following commands to set the active kernel parameters:
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
Default Value
accept_ra is enabled (set to 1) by default.
References
- 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