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3.3.2.7 Ensure net.ipv6.conf.all.accept_ra is configured

Information

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 controls accepting any IPv6 RA messages on any network device.

Note: If IPv6 has been disabled, this recommendation is not applicable.

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.

Solution

- Review all files being used by systemd sysctl and comment out or remove all net.ipv6.conf.all.accept_ra lines that are not net.ipv6.conf.all.accept_ra=0.

Example script:

#!/usr/bin/env bash

{
 l_option="net.ipv6.conf.all.accept_ra" l_value="0"
 l_grep="${l_option//./(\\.|\\/)}" a_files=()
 l_systemdsysctl="$(readlink -e /lib/systemd/systemd-sysctl \
 || readlink -e /usr/lib/systemd/systemd-sysctl)"
 l_ufw_file="$([ -f /etc/default/ufw ] && \
 awk -F= '/^\s*IPT_SYSCTL=/ {print $2}' /etc/default/ufw)"
 [ -f "$(readlink -e "$l_ufw_file")" ] && \
 a_files+=("$l_ufw_file"); a_files+=("/etc/sysctl.conf")
 while IFS= read -r l_fname; do
 l_file="$(readlink -e "${l_fname//# /}")"
 [ -n "$l_file" ] && ! grep -Psiq -- '(^|\h+)'"$l_file"'\b' \
 <<< "${a_files[*]}" && a_files+=("$l_file")
 done < <("$l_systemdsysctl" --cat-config | tac | \
 grep -Pio -- '^\h*#\h*\/[^#\n\r\h]+\.conf\b')
 for l_file in "${a_files[@]}"; do
 grep -Poi -- '\h*'"$l_grep"'\h*=\h*\H+\b' "$l_file" \
 | grep -Pivq -- '^\h*'"$l_grep"'\h*=\h*'"$l_value"'\b' && \
 sed -ri '/^\s*'"$l_grep"'\s*=\s*(1[0-9]*)/s/^/# /' "$l_file"
 done
}
 - Create or edit a file in the /etc/sysctl.d/ directory ending in .conf and edit or add the following line:

net.ipv6.conf.all.accept_ra = 0

Example:

# [ ! -d "/etc/sysctl.d/" ] && mkdir -p /etc/sysctl.d/
# printf '%s\n' "" "net.ipv6.conf.all.accept_ra = 0" >> /etc/sysctl.d/60-ipv6_sysctl.conf

Note: If the UFW file was the first file listed in the audit, the entry will be commented out as part of the first step, however updating Uncomplicated Firewall (UFW) may update this change. In this case the updated entry will supersede the entry being created as part of this step.

 - Run the following command to load all sysctl configuration filles:

# sysctl --system

See Also

https://workbench.cisecurity.org/benchmarks/24008

Item Details

Category: CONFIGURATION MANAGEMENT

References: 800-53|CM-6b., CSCv7|9.2

Plugin: Unix

Control ID: f27bb0ad0f6bb3cc62255b88088e1c69e6c24a9a12e2c41f2890f1cc0f859d51