cis-ubuntu2004-v300-5-1-9

name	cis-ubuntu2004-v300-5-1-9
description	Ensure sshd GSSAPIAuthentication is disabled
category	cis-networking
version	3.0.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-20.04","ssh"]
cis_id	5.1.9
cis_benchmark	CIS Ubuntu Linux 20.04 LTS Benchmark v3.0.0
tech_stack	["ubuntu","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

Ensure sshd GSSAPIAuthentication is disabled (Automated)

Profile Applicability

• Level 1 - Workstation
• Level 2 - Server

Description

The GSSAPIAuthentication parameter specifies whether user authentication based on GSSAPI is allowed.

Rationale

Allowing GSSAPI authentication through SSH exposes the system's GSSAPI to remote hosts, and should be disabled to reduce the attack surface of the system.

Audit Procedure

Command Line

Run the following command to verify GSSAPIAuthentication is set to no:

# sshd -T | grep gssapiauthentication

gssapiauthentication no

• IF - Match set statements are used in your environment, specify the connection parameters to use for the -T extended test mode and run the audit to verify the setting is not incorrectly configured in a match block. Example additional audit needed for a match block for the user sshuser:

# sshd -T -C user=sshuser | grep gssapiauthentication

Note: If provided, any Match directives in the configuration file that would apply are applied before the configuration is written to standard output. The connection parameters are supplied as keyword=value pairs and may be supplied in any order, either with multiple -C options or as a comma-separated list. The keywords are addr (source address), user (user), host (resolved source host name), laddr (local address), lport (local port number), and rdomain (routing domain)

Expected Result

gssapiauthentication no

Remediation

Command Line

Edit the /etc/ssh/sshd_config file to set the GSSAPIAuthentication parameter to no above any Include and Match entries as follows:

GSSAPIAuthentication no

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 location.