Ensure secure ICMP redirects are not accepted

LowLevel 2Automatedbottlerocket

Description

Secure ICMP redirects are the same as ICMP redirects, except they come from gateways listed on the default gateway list. It is assumed that these gateways are known to your system, and that they are likely to be secure. The audit reads the running values 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 $2)"; bad=1; }; }
chk net.ipv4.conf.all.secure_redirects 0
chk net.ipv4.conf.default.secure_redirects 0
[ "$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 parameters and persist the settings: # apiclient apply <<EOF [settings.kernel.sysctl] "net.ipv4.conf.all.secure_redirects" = "0" "net.ipv4.conf.default.secure_redirects" = "0" 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 - 3.2.3 Ensure secure ICMP redirects are not accepted

Check this host

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

shell

tmaegis scan --target bottlerocket --level 2