Suspicious Rundll32 Rename

SPLUNK detection rule by Michael Haag, Splunk · Apache-2.0

The following hunting analytic identifies renamed instances of rundll32.exe executing. rundll32.exe is natively found in C:\Windows\system32 and C:\Windows\syswow64. During investigation, validate it is the legitimate rundll32.exe executing and what script content it is loading. This query relies on the original filename or internal name from the PE meta data. Expand the query as needed by looking for specific command line arguments outlined in other analytics.

name: Suspicious Rundll32 Rename
id: 7360137f-abad-473e-8189-acbdaa34d114
version: 8
creation_date: '2021-01-15'
modification_date: '2026-05-13'
author: Michael Haag, Splunk
status: removed
type: Hunting
description: The following hunting analytic identifies renamed instances of rundll32.exe executing. rundll32.exe is natively found in C:\Windows\system32 and C:\Windows\syswow64. During investigation, validate it is the legitimate rundll32.exe executing and what script content it is loading. This query relies on the original filename or internal name from the PE meta data. Expand the query as needed by looking for specific command line arguments outlined in other analytics.
data_source:
    - Sysmon EventID 1
search: '| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where Processes.original_file_name=RUNDLL32.exe AND Processes.process_name!=rundll32.exe by Processes.dest Processes.user Processes.parent_process_name Processes.process_name Processes.process Processes.process_id Processes.parent_process_id Processes.original_file_name | `drop_dm_object_name(Processes)` | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `suspicious_rundll32_rename_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: Although unlikely, some legitimate applications may use a moved copy of rundll32, triggering a false positive.
references:
    - https://attack.mitre.org/techniques/T1218/011/
    - https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1218.011/T1218.011.md
    - https://lolbas-project.github.io/lolbas/Binaries/Rundll32/
tags:
    analytic_story:
        - Suspicious Rundll32 Activity
        - Masquerading - Rename System Utilities
    asset_type: Endpoint
    mitre_attack_id:
        - T1036.003
        - T1218.011
    product:
        - Splunk Enterprise
        - Splunk Enterprise Security
        - Splunk Cloud
    security_domain: endpoint
deprecation_info:
    reason: Detection deprecated as it no longer effectively identifies the intended malicious activity
    removed_in_version: 5.2.0
    replacement_content: []

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1b1d24ab-b2b8-4482-9e6e-665e9bdd99b3

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Executable code, not a declarative rule

This submission is arbitrary [[ currentRule.format ? currentRule.format.toUpperCase() : '' ]] code, not a declarative detection rule — review it as you would any script before running it, and note that it cannot be safely aggregated or auto-executed alongside YARA/Sigma/Suricata/CRS rules.

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Format & documentation suggestions

Not a security issue — this rule is valid and was accepted as-is. These are optional fields/conventions its own format recommends, mainly affecting its quality score and how well it documents itself for other reviewers.

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