Ensure sshd DisableForwarding is enabled

MediumLevel 1Automatedlinux

Description

The DisableForwarding parameter disables all forwarding features, including X11, ssh-agent(1), TCP and StreamLocal. This option overrides all other forwarding-related options and may simplify restricted configurations. • X11Forwarding provides the ability to tunnel X11 traffic through the connection to enable remote graphic connections. • ssh-agent is a program to hold private keys used for public key authentication. Through use of environment variables the agent can be located and automatically used for authentication when logging in to other machines using ssh. • SSH port forwarding is a mec

How it is checked

Audit method: Shell command

shell

alt0() { command -v grep >/dev/null 2>&1 || { echo "step1: grep not installed"; return 1; }; command -v sshd >/dev/null 2>&1 || { echo "step1: sshd not installed"; return 1; }; o=$(bash -c 'sshd -T | grep -i disableforwarding' 2>&1); printf '%s\n' "$o" | tr -s ' \t' '  ' | sed 's/^ //;s/ $//' | grep -Fxq -- 'disableforwarding yes' || { echo step1: missing 'disableforwarding yes'; return 1; }; }; if alt0; then echo compliant; fi

Expected output: compliant

How it is fixed

Fix method: Guidance or infrastructure patch

Edit the /etc/ssh/sshd_config file to set the DisableForwarding parameter to yes above any Include entry as follows: DisableForwarding yes Note: First occurrence of an option takes precedence, Match set statements withstanding. If Include locations are enabled, used, and order of precedence is understood in your environment, the entry may be created in a file in Include location.

Properties

Operating systems: rhel-10
Tags: cis-convertedlinux
Reference: CIS Red Hat Enterprise Linux 10 Benchmark v1.0.1 - 5.1.8

Check this host

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

shell

tmaegis scan --target linux