Detection: Linux Auditd Disable Or Modify System Firewall

Description

The following analytic detects the suspicious disable or modify system firewall. This behavior is critical for a SOC to monitor because it may indicate attempts to gain unauthorized access or maintain control over a system. Such actions could be signs of malicious activity. If confirmed, this could lead to serious consequences, including a compromised system, unauthorized access to sensitive data, or even a wider breach affecting the entire network. Detecting and responding to these signs early is essential to prevent potential security incidents.

Search

1`linux_auditd` type=SERVICE_STOP unit IN ("firewalld", "ufw") 
2| rename host as dest 
3| stats count min(_time) as firstTime max(_time) as lastTime by type pid UID comm exe unit dest 
4| `security_content_ctime(firstTime)`
5| `security_content_ctime(lastTime)`
6| `linux_auditd_disable_or_modify_system_firewall_filter`

Data Source

Name	Platform	Sourcetype	Source
Linux Auditd Service Stop	Linux	'linux:audit'	'/var/log/audit/audit.log'

Macros Used

Annotations

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Implementation

To implement this detection, the process begins by ingesting auditd data, that consist SYSCALL, TYPE, EXECVE and PROCTITLE events, which captures command-line executions and process details on Unix/Linux systems. These logs should be ingested and processed using Splunk Add-on for Unix and Linux (https://splunkbase.splunk.com/app/833), which is essential for correctly parsing and categorizing the data. The next step involves normalizing the field names to match the field names set by the Splunk Common Information Model (CIM) to ensure consistency across different data sources and enhance the efficiency of data modeling. This approach enables effective monitoring and detection of linux endpoints where auditd is deployed

Known False Positives

Administrator or network operator can use this application for automation purposes. Please update the filter macros to remove false positives.

Associated Analytic Story

• Compromised Linux Host

• Linux Living Off The Land

• Linux Persistence Techniques

• Linux Privilege Escalation

Risk Based Analytics (RBA)

References

• https://www.splunk.com/en_us/blog/security/deep-dive-on-persistence-privilege-escalation-technique-and-detection-in-linux-platform.html

Detection Testing

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub | Version: 2