cis-ubuntu1604-v200-5-1-9

DevOps & Security

Ensure at is restricted to authorized users

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Source SKILL.md: https://github.com/CyberStrikeus/CyberStrike/blob/HEAD/.cyberstrike/skill/CIS_benchmarks/Operating_Systems/Ubuntu/CIS_Ubuntu_Linux_16.04_LTS_Benchmark_v2.0.0/cis-ubuntu1604-v200-5-1-9/SKILL.md

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CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0 - 5.1.9

Profile Applicability

Level 1 - Server
Level 1 - Workstation

Description

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

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

Rationale

On many systems, only the system administrator is authorized to schedule at jobs. Using the at.allow file to control who can run at 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/at.deny does not exist:

stat /etc/at.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/at.allow:

stat /etc/at.allow

Expected Result

The first command should return:

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

The second command should return:

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

Remediation

Command Line

Run the following commands to remove /etc/at.deny:

rm /etc/at.deny

Run the following command to create /etc/at.allow:

touch /etc/at.allow

Run the following commands to set permissions and ownership for /etc/at.allow:

chmod g-wx,o-rwx /etc/at.allow
chown root:root /etc/at.allow

Default Value

By default, /etc/at.deny exists and /etc/at.allow does not exist.

References

None.

CIS Controls

Controls Version	Control
v7	14.6 Protect Information through Access Control Lists

Assessment Status

Automated