Regsvr32 Silent and Install Param Dll Loading

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

The following analytic detects the loading of a DLL using the regsvr32 application with the silent parameter and DLLInstall execution. It leverages data from Endpoint Detection and Response (EDR) agents, focusing on process command-line arguments and parent process details. This activity is significant as it is commonly used by RAT malware like Remcos and njRAT to load malicious DLLs on compromised machines. If confirmed malicious, this technique could allow attackers to execute arbitrary code, maintain persistence, and further compromise the system.

name: Regsvr32 Silent and Install Param Dll Loading
id: f421c250-24e7-11ec-bc43-acde48001122
version: 15
creation_date: '2021-10-04'
modification_date: '2026-06-09'
author: Teoderick Contreras, Splunk
status: production
type: Anomaly
description: The following analytic detects the loading of a DLL using the regsvr32 application with the silent parameter and DLLInstall execution. It leverages data from Endpoint Detection and Response (EDR) agents, focusing on process command-line arguments and parent process details. This activity is significant as it is commonly used by RAT malware like Remcos and njRAT to load malicious DLLs on compromised machines. If confirmed malicious, this technique could allow attackers to execute arbitrary code, maintain persistence, and further compromise the system.
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_regsvr32`
    Processes.process  IN ("*/i*", "*-i*")
    Processes.process  IN ("*/s*", "*-s*")
    NOT Processes.process="*Microsoft\\TeamsMeetingAddin*"

    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)`
    | `regsvr32_silent_and_install_param_dll_loading_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: |
    Other third part application may used this parameter.
    One identified use case is Microsoft Teams. Apply the necessary filters before using this rule in production.
references:
    - https://app.any.run/tasks/dc93ee63-050c-4ff8-b07e-8277af9ab939/
    - https://attack.mitre.org/techniques/T1218/010/
drilldown_searches:
    - name: View the detection results for - "$user$" and "$dest$"
      search: '%original_detection_search% | search  user = "$user$" dest = "$dest$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$user$" and "$dest$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user$", "$dest$") | 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: user
          type: user
          score: 20
          message: An instance of $parent_process_name$ spawning $process_name$ was identified on endpoint $dest$ by user $user$ attempting to load a DLL using the silent and dllinstall parameter.
        - field: dest
          type: system
          score: 20
          message: An instance of $parent_process_name$ spawning $process_name$ was identified on endpoint $dest$ by user $user$ attempting to load a DLL using the silent and dllinstall parameter.
threat_objects:
    - field: parent_process_name
      type: parent_process_name
    - field: process_name
      type: process_name
analytic_story:
    - AsyncRAT
    - Hermetic Wiper
    - Living Off The Land
    - Data Destruction
    - Remcos
    - Suspicious Regsvr32 Activity
asset_type: Endpoint
mitre_attack_id:
    - T1218.010
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/T1059.005/vbs_wscript/sysmon.log
          source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
          sourcetype: XmlWinEventLog
      test_type: unit

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3576eea5-c8b5-4df5-a328-50218b065579

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