6.1.1 Audit system file permissions (Not Scored)

Level 2 - Server
Level 2 - Workstation 

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 rpm -qf command can be used to determine which package a particular file belongs to. For example the following commands determines which package the /bin/bash file belongs to:

# rpm -qf /bin/bash 

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

# rpm -V bash-4.1.2-29.el6.x86_64 
.M....... /bin/bash

Note that you can feed the output of the rpm -qf command to the rpm -V command:

# rpm -V `rpm -qf /etc/passwd` 
.M...... c /etc/passwd 
S.5....T c /etc/printcap

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.

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.

# rpm -Va --nomtime --nosize --nomd5 --nolinkto > <filename>

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

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 scorable 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.

  • centos7/6/1/1.txt
  • Last modified: 2017/05/04 19:50
  • by Piotr Kłoczewski