cis-ubuntu1604-v200-5-1-8

name	cis-ubuntu1604-v200-5-1-8
description	Ensure cron is restricted to authorized users
category	cis-iam
version	2.0.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-16.04","access-control"]
cis_id	5.1.8
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 - 5.1.8

Profile Applicability

• Level 1 - Server
• Level 1 - Workstation

Description

Configure /etc/cron.allow to allow specific users to use this 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.

Notes:

• Other methods, such as systemd timers, exist for scheduling jobs. If another method is used, cron should be removed, and the alternate method should be secured in accordance with local site policy
• 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.

Impact

None.

Audit Procedure

Command Line

Run the following command and verify that /etc/cron.deny does not exist:

stat /etc/cron.deny

Run the following command and verify Uid and Gid are both 0/root and Access, does not grant write or execute to group, and does not grant permissions to other for /etc/cron.allow:

stat /etc/cron.allow

Expected Result

The first command should return:

stat: cannot stat '/etc/cron.deny': No such file or directory

The second command should return:

Access: (0640/-rw-r-----)  Uid: (    0/    root)  Gid: (    0/    root)

Remediation

Command Line