Detection: Unload Sysmon Filter Driver

Description

The following analytic detects the use of fltMC.exe to unload the Sysmon driver, which stops Sysmon from collecting data. It leverages Endpoint Detection and Response (EDR) logs, focusing on process names and command-line executions. This activity is significant because disabling Sysmon can blind security monitoring, allowing malicious actions to go undetected. If confirmed malicious, this could enable attackers to execute further attacks without being logged, leading to potential data breaches, privilege escalation, or persistent access within the environment.

Search

1
2| tstats `security_content_summariesonly` count min(_time) as firstTime values(Processes.process) as process max(_time) as lastTime from datamodel=Endpoint.Processes where Processes.process_name=fltMC.exe AND Processes.process=*unload* AND Processes.process=*SysmonDrv*  by Processes.process_name Processes.process_id Processes.parent_process_name Processes.process Processes.dest Processes.user 
3| `drop_dm_object_name("Processes")` 
4| `security_content_ctime(firstTime)`
5|`security_content_ctime(lastTime)` 
6| table firstTime lastTime dest user count process_name process_id parent_process_name process 
7| `unload_sysmon_filter_driver_filter`

Data Source

Name	Platform	Sourcetype	Source
CrowdStrike ProcessRollup2	N/A	'crowdstrike:events:sensor'	'crowdstrike'
Sysmon EventID 1	Windows	'xmlwineventlog'	'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'
Windows Event Log Security 4688	Windows	'xmlwineventlog'	'XmlWinEventLog:Security'

Macros Used

Annotations

Default Configuration

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

Implementation

The detection is based on data that originates from Endpoint Detection and Response (EDR) agents. These agents are designed to provide security-related telemetry from the endpoints where the agent is installed. To implement this search, you must ingest logs that contain the process GUID, process name, and parent process. Additionally, you must ingest complete command-line executions. These logs must be processed using the appropriate Splunk Technology Add-ons that are specific to the EDR product. The logs must also be mapped to the Processes node of the Endpoint data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process.

Known False Positives

Unknown at the moment

Associated Analytic Story

• CISA AA23-347A

• Disabling Security Tools

Risk Based Analytics (RBA)

References

• https://www.ired.team/offensive-security/defense-evasion/unloading-sysmon-driver

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: 6