cis-ubuntu1604-v200-5-3-8

name	cis-ubuntu1604-v200-5-3-8
description	Ensure SSH MaxAuthTries is set to 4 or less
category	cis-networking
version	2.0.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-16.04","ssh","remote-access"]
cis_id	5.3.8
cis_benchmark	CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0
tech_stack	["ubuntu","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0 - Control 5.3.8

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 output MaxAuthTries is 4 or less:

sshd -T -C user=root -C host="$(hostname)" -C addr="$(grep $(hostname) /etc/hosts | awk '{print $1}')" | grep maxauthtries

Expected Result

maxauthtries 4

Run the following command and verify that the output:

grep -Ei '^\s*maxauthtries\s+([5-9]|[1-9][0-9]+)' /etc/ssh/sshd_config

Nothing is returned.

Remediation

Command Line

Edit the /etc/ssh/sshd_config file to set the parameter as follows:

MaxAuthTries 4

Default Value

MaxAuthTries 6

References

1. SSHD_CONFIG(5)

CIS Controls

Version 7

16.13 Alert on Account Login Behavior Deviation - Alert when users deviate from normal login behavior, such as time-of-day, workstation location and duration.

Profile Applicability

• Level 1 - Server
• Level 1 - Workstation

Assessment Status

Automated