Ensure broadcast ICMP requests are ignored

MediumLevel 1Automatedbottlerocket

Description

Setting net.ipv4.icmp_echo_ignore_broadcasts to 1 will cause the system to ignore all ICMP echo and timestamp requests to broadcast and multicast addresses. The audit reads the running value from /proc/sys. Run tmaegis on the host through the admin container root shell (sudo sheltie).

How it is checked

Audit method: Shell command

shell

bad=0
chk() { f=/proc/sys/$(printf %s "$1" | tr . /); v=$(cat "$f" 2>/dev/null) || { echo "$1: not readable"; bad=1; return; }; [ "$v" = "$2" ] || { echo "$1 = $v (expected $2)"; bad=1; }; }
chk net.ipv4.icmp_echo_ignore_broadcasts 1
[ "$bad" -eq 0 ] && echo compliant

Expected output: compliant

How it is fixed

Fix method: Guidance or infrastructure patch

Run the following command to set the active kernel parameter and persist the setting: # apiclient apply <<EOF [settings.kernel.sysctl] "net.ipv4.icmp_echo_ignore_broadcasts" = "1" EOF Run the following command to flush the routing cache: # sysctl -w net.ipv4.route.flush=1

Properties

Operating systems: Any
Tags: bottlerocketnetwork
Reference: CIS Bottlerocket Benchmark v1.0.0 - 3.2.5 Ensure broadcast ICMP requests are ignored

Check this host

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

shell

tmaegis scan --target bottlerocket