Windows Rundll32 Apply User Settings Changes
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.
Query · spl
| tstats `security_content_summariesonly`
count min(_time) as firstTime
max(_time) as lastTime
from datamodel=Endpoint.Processes where
`process_rundll32`
Processes.process = "*user32.dll*"
Processes.process = "*UpdatePerUserSystemParameters*"
by Processes.action Processes.dest Processes.original_file_name Processes.parent_process
Processes.parent_process_exec Processes.parent_process_guid Processes.parent_process_id
Processes.parent_process_name Processes.parent_process_path Processes.process Processes.process_exec
Processes.process_guid Processes.process_hash Processes.process_id Processes.process_integrity_level
Processes.process_name Processes.process_path Processes.user Processes.user_id Processes.vendor_product
| `drop_dm_object_name(Processes)`
| `security_content_ctime(firstTime)`
| `security_content_ctime(lastTime)`
| `windows_rundll32_apply_user_settings_changes_filter`
Implementation guide
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
- No false positives have been identified at this time.
Analyst notes
Known false positives: No false positives have been identified at this time.