Linux distributions
TMA-SLES11-3.2.2
Ensure ICMP redirects are not accepted
Description
ICMP redirect messages are packets that convey routing information and tell your host (acting as a router) to send packets via an alternate path. It is a way of allowing an outside routing device to update your system routing tables. By setting net.ipv4.conf.all.accept_redirects to 0, the system will not accept any ICMP redirect messages, and therefore, won't allow outsiders to update the system's routing tables.
How it is checked
Audit method: Shell command
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_redirects 0 && chk net.ipv4.conf.default.accept_redirects 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_redirects = 0 net.ipv4.conf.default.accept_redirects = 0 Run the following commands to set the active kernel parameters: # sysctl -w net.ipv4.conf.all.accept_redirects=0 # sysctl -w net.ipv4.conf.default.accept_redirects=0 # sysctl -w net.ipv4.route.flush=1
Properties
- Operating systems
- sles-11
- Tags
- cis-convertedkernellinuxsysctl
- Reference
- CIS SUSE Linux Enterprise 11 Benchmark v2.1.1 - 3.2.2
Check this host
Run this on a machine you are allowed to audit. The scan is read-only.
tmaegis scan --target linux