Detection: Windows Rundll32 Apply User Settings Changes

Updated Date: 2025-10-07 ID: b9fb8d97-dbc9-4a09-804c-ff0e3862bb2d Author: Teoderick Contreras, Nasreddine Bencherchali, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic detects the execution of rundll32 with a call to the user32 DLL, specifically the UpdatePerUserSystemParameters function. This function is responsible for updating 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. This activity can be significant as it is an uncommon way to apply settings. It was also observed as part of Rhysida Ransomware activity. 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` 
 3  count min(_time) as firstTime 
 4        max(_time) as lastTime 
 5        
 6from datamodel=Endpoint.Processes where 
 7
 8`process_rundll32`
 9Processes.process = "*user32.dll*"
10Processes.process = "*UpdatePerUserSystemParameters*" 
11
12by Processes.action Processes.dest Processes.original_file_name Processes.parent_process 
13   Processes.parent_process_exec Processes.parent_process_guid Processes.parent_process_id 
14   Processes.parent_process_name Processes.parent_process_path Processes.process Processes.process_exec 
15   Processes.process_guid Processes.process_hash Processes.process_id Processes.process_integrity_level 
16   Processes.process_name Processes.process_path Processes.user Processes.user_id Processes.vendor_product
17
18
19| `drop_dm_object_name(Processes)` 
20
21| `security_content_ctime(firstTime)` 
22
23| `security_content_ctime(lastTime)`
24
25| `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

Name	Value
process_rundll32	`(Processes.process_name=rundll32.exe OR Processes.original_file_name=RUNDLL32.EXE)`
windows_rundll32_apply_user_settings_changes_filter	`search *`

windows_rundll32_apply_user_settings_changes_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1218.011	Rundll32	Defense Evasion

Exploitation

DE.AE

CIS 10

Default Configuration

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

Setting	Value
Disabled	true
Cron Schedule	`0 * * * *`
Earliest Time	`-70m@m`
Latest Time	`-10m@m`
Schedule Window	`auto`
Creates Risk Event	True

This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

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)

Risk Message:

Process $process_name$ with cmdline $process$ in host $dest$

Risk Object	Risk Object Type	Risk Score	Threat Objects
dest	system	25	process_name

References

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`XmlWinEventLog:Microsoft-Windows-Sysmon/Operational`	`XmlWinEventLog`
Integration	✅ Passing	Dataset	`XmlWinEventLog:Microsoft-Windows-Sysmon/Operational`	`XmlWinEventLog`

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: 8