cis-ubuntu1604-v200-6-1-1

DevOps & Security

Audit system file permissions

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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-v200-6-1-1/SKILL.md

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CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0 - 6.1.1

Profile Applicability

Level 2 - Server
Level 2 - Workstation

Description

The Debian package manager has a number of useful options. One of these, the --verify option, can be used to verify that system packages are correctly installed. The --verify option can be used to verify a particular package or to verify all system packages. If no output is returned, the package is installed correctly. The following table describes the meaning of output from the verify option:

Code	Meaning
S	File size differs.
M	File mode differs (includes permissions and file type).
5	The MD5 checksum differs.
D	The major and minor version numbers differ on a device file.
L	A mismatch occurs in a link.
U	The file ownership differs.
G	The file group owner differs.
T	The file time (mtime) differs.

The dpkg -S command can be used to determine which package a particular file belongs to. For example the following command determines which package the /bin/bash file belongs to:

# dpkg -S /bin/bash
bash: /bin/bash

To verify the settings for the package that controls the /bin/bash file, run the following:

# dpkg --verify bash
??5?????? c /etc/bash.bashrc

Notes:

Since packages and important files may change with new updates and releases, it is recommended to verify everything, not just a finite list of files. This can be a time consuming task and results may depend on site policy therefore it is not a assessed benchmark item, but is provided for those interested in additional security measures.
Some of the recommendations of this benchmark alter the state of files audited by this recommendation. The audit command will alert for all changes to a file permissions even if the new state is more secure than the default.

Rationale

It is important to confirm that packaged system files and directories are maintained with the permissions they were intended to have from the OS vendor.

Audit Procedure

Command Line

Run the following command to review all installed packages. Note that this may be very time consuming and may be best scheduled via the cron utility. It is recommended that the output of this command be redirected to a file that can be reviewed later.

dpkg --verify <package name>

Expected Result

No output should be returned if the package is installed correctly.

Remediation

Command Line

Correct any discrepancies found and rerun the audit until output is clean or risk is mitigated or accepted.

Default Value

Not applicable.

References

CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0

CIS Controls

Controls Version	Control
v7	14.6 Protect Information through Access Control ListsProtect all information stored on systems with file system, network share, claims, application, or database specific access control lists. These controls will enforce the principle that only authorized individuals should have access to the information based on their need to access the information as a part of their responsibilities.

Assessment Status

Manual