cis-ubuntu1204-v110-11-2

name	cis-ubuntu1204-v110-11-2
description	Remove OS Information from Login Warning Banners
category	cis-os-hardening
version	1.1.0
author	cyberstrike-official
tags	["cis","ubuntu",12.04,"linux","banner","os-info","information-disclosure"]
cis_id	11.2
cis_benchmark	CIS Ubuntu 12.04 LTS Server Benchmark v1.1.0
tech_stack	["ubuntu","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

11.2 Remove OS Information from Login Warning Banners (Scored)

Profile Applicability

• Level 1

Description

Unix-based systems have typically displayed information about the OS release and patch level upon logging in to the system. This information can be useful to developers who are developing software for a particular OS platform. If mingetty(8) supports the following options, they display operating system information:

• \m - machine architecture (uname -m)
• \r - operating system release (uname -r)
• \s - operating system name
• \v - operating system version (uname -v)

Rationale

Displaying OS and patch level information in login banners also has the side effect of providing detailed system information to attackers attempting to target specific exploits of a system. Authorized users can easily get this information by running the uname -a command once they have logged in.

Audit Procedure

Using Command Line

Perform the following commands to check if OS information is set to be displayed in the system login banners:

egrep '(\\v|\\r|\\m|\\s)' /etc/issue
egrep '(\\v|\\r|\\m|\\s)' /etc/motd
egrep '(\\v|\\r|\\m|\\s)' /etc/issue.net

Expected Result

No output should be returned from any of the commands, indicating that no OS information escape sequences are present in the banner files.

Remediation

Using Command Line

Edit the /etc/motd, /etc/issue and /etc/issue.net files and remove any lines containing \m, \r, \s or \v.

Default Value

The default Ubuntu banner files may contain OS information escape sequences.

References

• CIS Ubuntu 12.04 LTS Server Benchmark v1.1.0

Profile

Level 1 - Scored