cyberstrikeus CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0 - Control 4.1.12
Profile
- Level: 2 - Server
- Level: 2 - Workstation
- Assessment Status: Automated
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.
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.
Impact
None.
Audit Procedure
Command Line
On a 32 bit system:
Run the following command to verify the rules are contained in a .rules file in the /etc/audit/rules.d/ directory:
grep mounts /etc/audit/rules.d/*.rules
Verify output matches:
-a always,exit -F arch=b32 -S mount -F auid>=1000 -F auid!=4294967295 -k mounts
Run the following command to verify that rules are in the running auditd config:
auditctl -l | grep mounts
Verify output matches:
-a always,exit -F arch=b32 -S mount -F auid>=1000 -F auid!=-1 -F key=mounts
On a 64 bit system:
Run the following command to verify the rules are contained in a .rules file in the /etc/audit/rules.d/ directory:
grep mounts /etc/audit/rules.d/*.rules
Verify output 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
Run the following command to verify that rules are in the running auditd config:
auditctl -l | grep mounts
Verify output matches:
-a always,exit -F arch=b64 -S mount -F auid>=1000 -F auid!=-1 -F key=mounts
-a always,exit -F arch=b32 -S mount -F auid>=1000 -F auid!=-1 -F key=mounts
Expected Result
Output should match the rules listed above for the appropriate architecture.
Remediation
Command Line
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 auid>=1000 with auid>=<UID_MIN for your system> in the Audit and Remediation procedures.
Default Value
By default, no audit rules are configured for mount events.
References
- CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0 - Section 4.1.12
CIS Controls
| Controls Version | Control |
|---|---|
| v7 | 5.1 Establish Secure Configurations - Maintain documented, standard security configuration standards for all authorized operating systems and software. |