Ensure default deny firewall policy

MediumLevel 1Automatedlinux

Description

A default deny all policy on connections ensures that any unconfigured network usage will be rejected.

How it is checked

Audit method: Shell command

shell

alt0() { command -v iptables >/dev/null 2>&1 || { echo "step1: iptables not installed"; return 1; }; o=$(bash -c 'iptables -L Chain INPUT (policy DROP)' 2>&1); printf '%s\n' "$o" | tr -s ' \t' '  ' | sed 's/^ //;s/ $//' | grep -Fxq -- 'Chain FORWARD (policy DROP)' || { echo step1: missing 'Chain FORWARD (policy DROP)'; return 1; }; printf '%s\n' "$o" | tr -s ' \t' '  ' | sed 's/^ //;s/ $//' | grep -Fxq -- 'Chain OUTPUT (policy DROP)' || { echo step1: missing 'Chain OUTPUT (policy DROP)'; return 1; }; }; if alt0; then echo compliant; fi

Expected output: compliant

How it is fixed

Fix method: Guidance or infrastructure patch

Run the following commands to implement a default DROP policy: # iptables -P INPUT DROP # iptables -P OUTPUT DROP # iptables -P FORWARD DROP # service iptables save

Properties

Operating systems: alinux-2
Tags: cis-convertedlinux
Reference: CIS Aliyun Linux 2 Benchmark v1.0.0 ARCHIVE - 3.5.1.1

Check this host

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

shell

tmaegis scan --target linux