cis-ubuntu2004-v300-2-2-4

name	cis-ubuntu2004-v300-2-2-4
description	Ensure telnet client is not installed
category	cis-networking
version	3.0.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-20.04","services","client","telnet"]
cis_id	2.2.4
cis_benchmark	CIS Ubuntu Linux 20.04 LTS Benchmark v3.0.0
tech_stack	["ubuntu","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

Ensure telnet client is not installed

Profile

• Level 1 - Server
• Level 1 - Workstation

Description

The telnet package contains the telnet client, which allows users to start connections to other systems via the telnet protocol.

Rationale

The telnet protocol is insecure and unencrypted. The use of an unencrypted transmission medium could allow an unauthorized user to steal credentials. The ssh package provides an encrypted session and stronger security and is included in most Linux distributions.

Impact

Many insecure service clients are used as troubleshooting tools and in testing environments. Uninstalling them can inhibit capability to test and troubleshoot. If they are required it is advisable to remove the clients after use to prevent accidental or intentional misuse.

Audit

Verify telnet is not installed. Use the following command to provide the needed information:

Command Line

# dpkg-query -s telnet &>/dev/null && echo "telnet is installed"

Expected Result

Nothing should be returned.

Remediation

Uninstall telnet:

Command Line

# apt purge telnet

References

1. NIST SP 800-53 Rev. 5: CM-7, CM-11

CIS Controls

Controls Version	Control	IG 1	IG 2	IG 3
v8	4.8 Uninstall or Disable Unnecessary Services on Enterprise Assets and Software Uninstall or disable unnecessary services on enterprise assets and software, such as an unused file sharing service, web application module, or service function.		●	●
v7	9.2 Ensure Only Approved Ports, Protocols and Services Are Running Ensure that only network ports, protocols, and services listening on a system with validated business needs, are running on each system.		●	●

MITRE ATT&CK Mappings

Techniques / Sub-techniques	Tactics	Mitigations
T1040, T1040.000, T1203, T1203.000, T1543, T1543.002	TA0006, TA0008	M1041, M1042