cis-ubuntu2004-v300-5-1-16

name	cis-ubuntu2004-v300-5-1-16
description	Ensure sshd MaxAuthTries is configured
category	cis-networking
version	3.0.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-20.04","ssh"]
cis_id	5.1.16
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 MaxAuthTries is configured (Automated)

Profile Applicability

• Level 1 - Server
• Level 1 - Workstation

Description

The MaxAuthTries parameter specifies the maximum number of authentication attempts permitted per connection. When the login failure count reaches half the number, error messages will be written to the syslog file detailing the login failure.

Rationale

Setting the MaxAuthTries parameter to a low number will minimize the risk of successful brute force attacks to the SSH server. While the recommended setting is 4, set the number based on site policy.

Audit Procedure

Command Line

Run the following command and verify that MaxAuthTries is 4 or less:

# sshd -T | grep maxauthtries

maxauthtries 4

• 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 maxauthtries

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

maxauthtries 4

(or a value of 4 or less)

Remediation

Command Line

Edit the /etc/ssh/sshd_config file to set the MaxAuthTries parameter to 4 or less above any Include and Match entries as follows:

MaxAuthTries 4