CIS Ubuntu 14.04 LTS - 4.1.13 Ensure successful file system mounts are collected

DevOps & Security

Collect audit events for mount system calls to detect media export activity

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4.1.13 Ensure successful file system mounts are collected (Scored)

Profile Applicability

Level 2 - Server
Level 2 - Workstation

Description

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.

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.

Audit Procedure

On a 32 bit system run the following commands:

grep mounts /etc/audit/audit.rules
auditctl -l | grep mounts

Verify output of both matches:

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

On a 64 bit system run the following commands:

grep mounts /etc/audit/audit.rules
auditctl -l | grep mounts

Verify output of both matches:

-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

Expected Result

The audit rules for mounts should be present and active.

Remediation

For 32 bit systems add the following lines to the /etc/audit/audit.rules file:

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

For 64 bit systems add the following lines to the /etc/audit/audit.rules file:

-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

Notes: 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 may require a system reboot.

Default Value

Not configured by default.

References

CIS Controls v6.1 - 13 Data Protection

Profile

Level 2 - Server
Level 2 - Workstation