Windows Rundll32 Apply User Settings Changes

SPLUNK detection rule by Teoderick Contreras, Nasreddine Bencherchali, Splunk · Apache-2.0

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.

name: Windows Rundll32 Apply User Settings Changes
id: b9fb8d97-dbc9-4a09-804c-ff0e3862bb2d
version: 13
creation_date: '2021-08-09'
modification_date: '2026-05-13'
author: Teoderick Contreras, Nasreddine Bencherchali, Splunk
status: production
type: Anomaly
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.
data_source:
    - Sysmon EventID 1
    - Windows Event Log Security 4688
    - CrowdStrike ProcessRollup2
search: |
    | 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`
how_to_implement: 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.
references:
    - https://www.cisa.gov/news-events/cybersecurity-advisories/aa23-319a
    - https://www.cisa.gov/sites/default/files/publications/aa22-264a-iranian-cyber-actors-conduct-cyber-operations-against-the-government-of-albania.pdf
    - https://cdn.pathfactory.com/assets/10555/contents/400686/13f4424c-05b4-46db-bb9c-6bf9b5436ec4.pdf
drilldown_searches:
    - name: View the detection results for - "$dest$"
      search: '%original_detection_search% | search  dest = "$dest$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$dest$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$dest$") | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
      earliest_offset: 7d
      latest_offset: "0"
intermediate_findings:
    entities:
        - field: dest
          type: system
          score: 20
          message: Process $process_name$ with cmdline $process$ in host $dest$
threat_objects:
    - field: process_name
      type: process_name
analytic_story:
    - Rhysida Ransomware
asset_type: Endpoint
mitre_attack_id:
    - T1218.011
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: endpoint
security_domain: endpoint
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1218.011/update_per_user_system/rundll32_updateperusersystem.log
          source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
          sourcetype: XmlWinEventLog
      test_type: unit

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1d6552d1-509c-413d-a84e-1994de4b7fbf

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