Detection: Windows Registry Delete Task SD

Description

The following analytic detects a process attempting to delete a scheduled task's Security Descriptor (SD) from the registry path of that task. It leverages the Endpoint.Registry data model to identify registry actions performed by the SYSTEM user, specifically targeting deletions or modifications of the SD value. This activity is significant as it may indicate an attempt to remove evidence of a scheduled task for defense evasion. If confirmed malicious, it suggests an attacker with privileged access trying to hide their tracks, potentially compromising system integrity and security. Immediate investigation is required.

Search

1
2| tstats `security_content_summariesonly` count from datamodel=Endpoint.Registry where Registry.registry_path IN ("*\\Schedule\\TaskCache\\Tree\\*") Registry.user="SYSTEM" Registry.registry_value_name="SD" (Registry.action=Deleted OR Registry.action=modified) by _time  Registry.dest Registry.process_guid Registry.user Registry.registry_path Registry.registry_value_name Registry.registry_key_name Registry.registry_value_data Registry.status Registry.action 
3| `drop_dm_object_name(Registry)` 
4| `security_content_ctime(firstTime)` 
5| `security_content_ctime(lastTime)` 
6| `windows_registry_delete_task_sd_filter`

Data Source

Name	Platform	Sourcetype	Source	Supported App
Sysmon EventID 12	Windows	'xmlwineventlog'	'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'	N/A

Macros Used

Annotations

Default Configuration

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

Implementation

To successfully implement this search you need to be ingesting information on process that include the name of the process responsible for the changes from your endpoints into the Endpoint datamodel in the Registry node. In addition, confirm the latest CIM App 4.20 or higher is installed and the latest TA for the endpoint product.

Known False Positives

False positives should be limited as the activity is not common to delete ONLY the SD from the registry. Filter as needed. Update the analytic Modified or Deleted values based on product that is in the datamodel.

Associated Analytic Story

• Scheduled Tasks

• Windows Persistence Techniques

• Windows Registry Abuse

Risk Based Analytics (RBA)

References

• https://www.microsoft.com/security/blog/2022/04/12/tarrask-malware-uses-scheduled-tasks-for-defense-evasion/

• https://gist.github.com/MHaggis/5f7fd6745915166fc6da863d685e2728

• https://gist.github.com/MHaggis/b246e2fae6213e762a6e694cabaf0c17

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