Ensure source routed packets are not accepted

MediumLevel 1Automatedlinux

Description

In networking, source routing allows a sender to partially or fully specify the route packets take through a network. In contrast, non-source routed packets travel a path determined by routers in the network. In some cases, systems may not be routable or reachable from some locations (e.g. private addresses vs. Internet routable), and so source routed packets would need to be used.

How it is checked

Audit method: Shell command

shell

chk() { p=$1; allowed=" $2 "; case $p in net.ipv6.*) [ -d /proc/sys/net/ipv6 ] || return 0;; esac; v=$(sysctl -n "$p" 2>/dev/null) || { echo "$p: not available"; return 1; }; case "$allowed" in *" $v "*) ;; *) echo "$p is $v (running)"; return 1;; esac; sd=$(readlink -e /lib/systemd/systemd-sysctl || readlink -e /usr/lib/systemd/systemd-sysctl); f=$("$sd" --cat-config 2>/dev/null | grep -Po "^\h*${p//./\.}\h*=\h*\K\H+" | tail -n1); [ -n "$f" ] || { echo "$p is not set in any sysctl configuration file"; return 1; }; case "$allowed" in *" $f "*) ;; *) echo "$p is $f in configuration"; return 1;; esac; }; if chk net.ipv4.conf.all.accept_source_route 0 && chk net.ipv4.conf.default.accept_source_route 0 && chk net.ipv6.conf.all.accept_source_route 0 && chk net.ipv6.conf.default.accept_source_route 0; then echo compliant; fi

Expected output: compliant

How it is fixed

Fix method: Guidance or infrastructure patch

Set the following parameters in /etc/sysctl.conf or a /etc/sysctl.d/* file: net.ipv4.conf.all.accept_source_route = 0 net.ipv4.conf.default.accept_source_route = 0 net.ipv6.conf.all.accept_source_route = 0 net.ipv6.conf.default.accept_source_route = 0 Run the following commands to set the active kernel parameters: # sysctl -w net.ipv4.conf.all.accept_source_route=0 # sysctl -w net.ipv4.conf.default.accept_source_route=0 # sysctl -w net.ipv6.conf.all.accept_source_route=0 # sysctl -w net.ipv6.conf.default.accept_source_route=0 # sysctl -w net.ipv4.route.flush=1 # sysctl -w net.ipv6.route.flush=1

Properties

Operating systems: alinux-2
Tags: cis-convertedkernellinuxsysctl
Reference: CIS Aliyun Linux 2 Benchmark v1.0.0 ARCHIVE - 3.2.1

Check this host

Run this on a machine you are allowed to audit. The scan is read-only.

shell

tmaegis scan --target linux