Detection: Windows Rundll32 Apply User Settings Changes

Description

The following analytic detects the execution of a suspicious rundll32 command line that updates user-specific system parameters, such as desktop backgrounds, display settings, and visual themes. It leverages data from Endpoint Detection and Response (EDR) agents, focusing on command-line executions involving "user32.dll,UpdatePerUserSystemParameters." This activity is significant as it is uncommon for legitimate purposes and has been observed in Rhysida Ransomware for defense evasion. If confirmed malicious, this could allow an attacker to disguise activities or make unauthorized system changes, potentially leading to persistent unauthorized access.

Search

1
2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where Processes.process_name=rundll32.exe Processes.process= "*user32.dll,UpdatePerUserSystemParameters*" by Processes.dest Processes.user Processes.parent_process Processes.process_name Processes.process Processes.process_id Processes.parent_process_id Processes.parent_process_name 
3| `drop_dm_object_name(Processes)` 
4| `security_content_ctime(firstTime)` 
5| `security_content_ctime(lastTime)` 
6| `windows_rundll32_apply_user_settings_changes_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

Associated Analytic Story

• Rhysida Ransomware

Risk Based Analytics (RBA)

References

• https://www.cisa.gov/news-events/cybersecurity-advisories/aa23-319a

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: 3