cyberstrikeus CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0 - Control 4.1.13
Profile
- Level: 2 - Server
- Level: 2 - Workstation
- Assessment Status: Automated
Description
Monitor the use of system calls associated with the deletion or renaming of files and file attributes. This configuration statement sets up monitoring for the unlink (remove a file), unlinkat (remove a file attribute), rename (rename a file) and renameat (rename a file attribute) system calls and tags them with the identifier "delete".
Note:
- At a minimum, configure the audit system to collect file deletion events for all users and root.
- Reloading the auditd config to set active settings requires the auditd service to be restarted, and may require a system reboot.
Rationale
Monitoring these calls from non-privileged users could provide a system administrator with evidence that inappropriate removal of files and file attributes associated with protected files is occurring. While this audit option will look at all events, system administrators will want to look for specific privileged files that are being deleted or altered.
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 delete /etc/audit/rules.d/*.rules
Verify output matches:
-a always,exit -F arch=b32 -S unlink -S unlinkat -S rename -S renameat -F auid>=1000 -F auid!=4294967295 -k delete
Run the following command to verify that rules are in the running auditd config:
auditctl -l | grep delete
Verify output matches:
-a always,exit -F arch=b32 -S unlink,rename,unlinkat,renameat -F auid>=1000 -F auid!=-1 -F key=delete
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 delete /etc/audit/rules.d/*.rules
Verify output matches:
-a always,exit -F arch=b64 -S unlink -S unlinkat -S rename -S renameat -F auid>=1000 -F auid!=4294967295 -k delete
-a always,exit -F arch=b32 -S unlink -S unlinkat -S rename -S renameat -F auid>=1000 -F auid!=4294967295 -k delete
Run the following command to verify that rules are in the running auditd config:
auditctl -l | grep delete
Verify output matches:
-a always,exit -F arch=b64 -S rename,unlink,unlinkat,renameat -F auid>=1000 -F auid!=-1 -F key=delete
-a always,exit -F arch=b32 -S unlink,rename,unlinkat,renameat -F auid>=1000 -F auid!=-1 -F key=delete
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-delete.rules
Add the following lines:
-a always,exit -F arch=b32 -S unlink -S unlinkat -S rename -S renameat -F auid>=1000 -F auid!=4294967295 -k delete
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-delete.rules
Add the following lines:
-a always,exit -F arch=b64 -S unlink -S unlinkat -S rename -S renameat -F auid>=1000 -F auid!=4294967295 -k delete
-a always,exit -F arch=b32 -S unlink -S unlinkat -S rename -S renameat -F auid>=1000 -F auid!=4294967295 -k delete
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 file deletion events.
References
- CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0 - Section 4.1.13
CIS Controls
| Controls Version | Control |
|---|---|
| v7 | 13 Data Protection - Data Protection |