Mshta spawning Rundll32 OR Regsvr32 Process

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

The following analytic detects a suspicious mshta.exe process spawning rundll32 or regsvr32 child processes. It leverages data from Endpoint Detection and Response (EDR) agents, focusing on process GUID, process name, and parent process fields. This activity is significant as it is a known technique used by malware like Trickbot to load malicious DLLs and execute payloads. If confirmed malicious, this behavior could allow attackers to execute arbitrary code, escalate privileges, or download additional malware, posing a severe threat to the environment.

name: Mshta spawning Rundll32 OR Regsvr32 Process
id: 4aa5d062-e893-11eb-9eb2-acde48001122
version: 14
creation_date: '2021-07-19'
modification_date: '2026-05-13'
author: Teoderick Contreras, Splunk
status: production
type: TTP
description: The following analytic detects a suspicious mshta.exe process spawning rundll32 or regsvr32 child processes. It leverages data from Endpoint Detection and Response (EDR) agents, focusing on process GUID, process name, and parent process fields. This activity is significant as it is a known technique used by malware like Trickbot to load malicious DLLs and execute payloads. If confirmed malicious, this behavior could allow attackers to execute arbitrary code, escalate privileges, or download additional malware, posing a severe threat to the environment.
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 Processes.parent_process_name = "mshta.exe"  `process_rundll32`
        OR
        `process_regsvr32`
      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)`
    | `mshta_spawning_rundll32_or_regsvr32_process_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: limitted. this anomaly behavior is not commonly seen in clean host.
references:
    - https://twitter.com/cyb3rops/status/1416050325870587910?s=21
drilldown_searches:
    - name: View the detection results for - "$dest$" and "$user$"
      search: '%original_detection_search% | search  dest = "$dest$" user = "$user$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$dest$" and "$user$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$dest$", "$user$") | 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"
finding:
    title: a mshta parent process $parent_process_name$ spawn child process $process_name$ in host $dest$
    entity:
        field: user
        type: user
        score: 50
intermediate_findings:
    entities:
        - field: dest
          type: system
          score: 50
          message: a mshta parent process $parent_process_name$ spawn child process $process_name$ in host $dest$
analytic_story:
    - Trickbot
    - IcedID
    - Living Off The Land
    - APT37 Rustonotto and FadeStealer
asset_type: Endpoint
mitre_attack_id:
    - T1218.005
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/malware/trickbot/spear_phish/windows-sysmon.log
          source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
          sourcetype: XmlWinEventLog
      test_type: unit

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