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4.1.12 Ensure successful file system mounts are collected - auditctl (32-bit)

Information

Monitor the use of the mount system call. The mount (and umount ) system call controls the mounting and unmounting of file systems. The parameters below configure the system to create an audit record when the mount system call is used by a non-privileged user

Note:

This tracks successful and unsuccessful mount commands. File system mounts do not have to come from external media and this action still does not verify write (e.g. CD ROMS).

Reloading the auditd config to set active settings requires the auditd service to be restarted, and may require a system reboot.

Rationale:

It is highly unusual for a non privileged user to mount file systems to the system. While tracking mount commands gives the system administrator evidence that external media may have been mounted (based on a review of the source of the mount and confirming it's an external media type), it does not conclusively indicate that data was exported to the media. System administrators who wish to determine if data were exported, would also have to track successful open , creat and truncate system calls requiring write access to a file under the mount point of the external media file system. This could give a fair indication that a write occurred. The only way to truly prove it, would be to track successful writes to the external media. Tracking write system calls could quickly fill up the audit log and is not recommended. Recommendations on configuration options to track data export to media is beyond the scope of this document.

Solution

For 32 bit systems Edit or create a file in the /etc/audit/rules.d/ directory ending in .rules
Example: vi /etc/audit/rules.d/50-mounts.rules
Add the following lines:

-a always,exit -F arch=b32 -S mount -F auid>=1000 -F auid!=4294967295 -k mounts

For 64 bit systems Edit or create a file in the /etc/audit/rules.d/ directory ending in .rules
Example: vi /etc/audit/rules.d/50-mounts.rules
Add the following lines:

-a always,exit -F arch=b64 -S mount -F auid>=1000 -F auid!=4294967295 -k mounts
-a always,exit -F arch=b32 -S mount -F auid>=1000 -F auid!=4294967295 -k mounts

Additional Information:

Systems may have been customized to change the default UID_MIN. To confirm the UID_MIN for your system, run the following command:

# awk '/^s*UID_MIN/{print $2}' /etc/login.defs

If your systems' UID_MIN is not 1000, replace audit>=1000 with audit>=<UID_MIN for your system> in the Audit and Remediation procedures.

See Also

https://workbench.cisecurity.org/files/3219

Item Details

Category: CONFIGURATION MANAGEMENT

References: 800-53|CM-6, CSCv7|5.1

Plugin: Unix

Control ID: d70614e65eee7767156fca23cae8dd56a614c772c8da435f05bdcc52525e6c93