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cis-ubuntu1204-v110-8-1-14

DevOps & Security
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Collect File Deletion Events by User

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Source SKILL.md: https://github.com/CyberStrikeus/CyberStrike/blob/HEAD/.cyberstrike/skill/CIS_benchmarks/Operating_Systems/Ubuntu/CIS_Ubuntu_12.04_LTS_Server_Benchmark_v1.1.0/cis-ubuntu1204-v110-8-1-14/SKILL.md

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8.1.14 Collect File Deletion Events by User (Scored)

Profile Applicability

  • Level 2

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".

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.

Audit Procedure

Using Command Line

For 64 bit systems, perform the following command and ensure the output is as shown to determine if file deletion events by user are recorded:

grep delete /etc/audit/audit.rules

For 32 bit systems:

grep delete /etc/audit/audit.rules

Expected Result

For 64 bit systems:

-a always,exit -F arch=b64 -S unlink -S unlinkat -S rename -S renameat -F auid>=500 -F auid!=4294967295 -k delete
-a always,exit -F arch=b32 -S unlink -S unlinkat -S rename -S renameat -F auid>=500 -F auid!=4294967295 -k delete

For 32 bit systems:

-a always,exit -F arch=b32 -S unlink -S unlinkat -S rename -S renameat -F auid>=500 -F auid!=4294967295 -k delete

Remediation

Using Command Line

At a minimum, configure the audit system to collect file deletion events for all users and root.

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

-a always,exit -F arch=b64 -S unlink -S unlinkat -S rename -S renameat -F auid>=500 -F auid!=4294967295 -k delete
-a always,exit -F arch=b32 -S unlink -S unlinkat -S rename -S renameat -F auid>=500 -F auid!=4294967295 -k delete
# Execute the following command to restart auditd
pkill -HUP -P 1 auditd

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

-a always,exit -F arch=b32 -S unlink -S unlinkat -S rename -S renameat -F auid>=500 -F auid!=4294967295 -k delete
# Execute the following command to restart auditd
pkill -HUP 1-HUP auditd

Default Value

By default, file deletion events by user are not audited.

References

  • CIS Ubuntu 12.04 LTS Server Benchmark v1.1.0

Profile

Level 2 - Scored