cis-ubuntu1604-v200-5-3-6

name	cis-ubuntu1604-v200-5-3-6
description	Ensure SSH LogLevel is appropriate
category	cis-networking
version	2.0.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-16.04","ssh","remote-access"]
cis_id	5.3.6
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 5.3.6

Description

INFO level is the basic level that only records login activity of SSH users. In many situations, such as Incident Response, it is important to determine when a particular user was active on a system. The logout record can eliminate those users who disconnected, which helps narrow the field.

VERBOSE level specifies that login and logout activity as well as the key fingerprint for any SSH key used for login will be logged. This information is important for SSH key management, especially in legacy environments.

Rationale

SSH provides several logging levels with varying amounts of verbosity. DEBUG is specifically not recommended other than strictly for debugging SSH communications since it provides so much data that it is difficult to identify important security information.

Audit Procedure

Command Line

Run the following command and verify that output matches loglevel VERBOSE or loglevel INFO:

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

Expected Result

loglevel VERBOSE or loglevel INFO

Run the following command and verify the output matches:

grep -i 'loglevel' /etc/ssh/sshd_config | grep -Evi '(VERBOSE|INFO)'

Nothing should be returned.

Remediation

Command Line

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

LogLevel VERBOSE

OR

LogLevel INFO

Default Value

LogLevel INFO

References

1. https://www.ssh.com/ssh/sshd_config/

CIS Controls

Version 7

6.2 Activate audit logging - Ensure that local logging has been enabled on all systems and networking devices.

6.3 Enable Detailed Logging - Enable system logging to include detailed information such as an event source, date, user, timestamp, source addresses, destination addresses, and other useful elements.