Vulnerability Discussion

Without generating audit records that are specific to the security and mission needs of the organization, it would be difficult to establish, correlate, and investigate the events relating to an incident or identify those responsible for one.

Audit records can be generated from various components within the information system (e.g., module or policy filter). The "crontab" command is used to maintain crontab files for individual users. Crontab is the program used to install, remove, or list the tables used to drive the cron daemon. This is similar to the task scheduler used in other operating systems.

When a user logs on, the AUID is set to the UID of the account that is being authenticated. Daemons are not user sessions and have the loginuid set to "-1". The AUID representation is an unsigned 32-bit integer, which equals "4294967295". The audit system interprets "-1", "4294967295", and "unset" in the same way.

Satisfies: SRG-OS-000062-GPOS-00031, SRG-OS-000037-GPOS-00015, SRG-OS-000042-GPOS-00020, SRG-OS-000062-GPOS-00031, SRG-OS-000392-GPOS-00172, SRG-OS-000462-GPOS-00206, SRG-OS-000471-GPOS-00215

Check

Verify that an audit event is generated for any successful/unsuccessful use of the "crontab" command by performing the following command to check the file system rules in "/etc/audit/audit.rules":

$ sudo grep -w crontab /etc/audit/audit.rules

-a always,exit -F path=/usr/bin/crontab -F perm=x -F auid>=1000 -F auid!=unset -k privileged-crontab

If the command does not return a line, or the line is commented out, this is a finding.

Fix

Configure the audit system to generate an audit event for any successful/unsuccessful uses of the "crontab" command by adding or updating the following rule in the "/etc/audit/rules.d/audit.rules" file:

-a always,exit -F path=/usr/bin/crontab -F perm=x -F auid>=1000 -F auid!=unset -k privileged-crontab

The audit daemon must be restarted for the changes to take effect.