cis-ubuntu1804-v220-4-1-8

name	cis-ubuntu1804-v220-4-1-8
description	Ensure cron is restricted to authorized users
category	cis-iam
version	2.2.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-18.04","cron","scheduling"]
cis_id	4.1.8
cis_benchmark	CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0
tech_stack	["ubuntu","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0 - Control 4.1.8

Profile Applicability

• Level 1 - Server
• Level 1 - Workstation

Description

Configure /etc/cron.allow to allow specific users to use the cron service. If /etc/cron.allow does not exist, then /etc/cron.deny is checked. Any user not specifically defined in this file is allowed to use cron. By removing the file, only users in /etc/cron.allow are allowed to use cron.

Note: Even though a given user is not listed in cron.allow, cron jobs can still be run as that user.

The cron.allow file only controls administrative access to the crontab command for scheduling and modifying cron jobs.

Rationale

On many systems, only the system administrator is authorized to schedule cron jobs. Using the cron.allow file to control who can run cron jobs enforces this policy. It is easier to manage an allow list than a deny list. In a deny list, you could potentially add a user ID to the system and forget to add it to the deny files.

Audit Procedure

Command Line

Run the following commands and verify that /etc/cron.deny does not exist, /etc/cron.allow exists, and the permissions and ownership are correct:

stat -c "%a %U %G" /etc/cron.allow
stat /etc/cron.deny

Expected Result

/etc/cron.allow should exist with permissions 640 or more restrictive, owned by root:root.

/etc/cron.deny should not exist (stat should return "No such file or directory").

Remediation

Command Line

Run the following commands to remove /etc/cron.deny, create /etc/cron.allow, and set the permissions:

rm -f /etc/cron.deny
touch /etc/cron.allow
chmod g-wx,o-rwx /etc/cron.allow
chown root:root /etc/cron.allow

References

1. NIST SP 800-53 Rev. 5: AC-3, MP-2

CIS Controls

v8 - 3.3 Configure Data Access Control Lists - Configure data access control lists based on a user's need to know. Apply data access control lists, also known as access permissions, to local and remote file systems, databases, and applications.