Windows rundll32 Process Creation With Uncommon DLL Extension in Command Line

Alerts on Windows rundll32 executions whose command lines lack common .cpl/.dll/.inf endings, indicating potential unusual invocation.

FreeReviewedSigma · Medium · v4

Product: windows
Category: process_creation
Author: Tim Shelton, Florian Roth (Nextron Systems), Yassine Oukessou (SigmaHQ), DRL 1.1
Published: 2022-01-13
Updated: 2026-10-18

Analysis Detection

ATT&CK techniques

Defense Evasion

Recon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
- T1218.011Rundll32
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule flags Windows process creation events where rundll32.exe is launched and the command line does not contain common file extensions commonly passed to rundll32 (e.g., .cpl, .dll, .inf), excluding specific known installer and update scenarios. Attackers may abuse rundll32 to load non-standard DLL or related files, blending execution into legitimate Windows tooling while evading expectations about typical extension usage. The detection relies on process creation telemetry including Image, OriginalFileName, ParentImage, and CommandLine content.

Reporting behind it

Related detections9 linkedT1218.011 — drag to rearrange

Suspicious Scheduled Task Executing Rundll32 DLL Export by Ordinal

Malicious Renamed Rundll32 Copied to Temp via Xcopy

Suspicious rundll32 Executing DLL from ProgramData (via process_creation)

Suspicious Rundll32 Loading DLL From Public or ProgramData Path via Process Creation (via process_creation)

Malicious LSASS Credential Dump via Rundll32 Comsvcs MiniDump via Process Creation (via process_creation)

Suspicious Rundll32 Execution Without a DLL Reference via Process Creation (via process_creation)

Suspicious WebDAV Retrieval via rundll32 and davclnt.dll (via process_creation)

Suspicious Rundll32 Execution with Latrodectus Loader Exports (via process_creation)

Suspicious Rundll32 Execution with IcedID Loader Export (via process_creation)

Windows rundll32 Process Creation With Uncommon DLL Extension in Command Line

Pivot detection · T1218.011 · 9 related

Changelog

v4
Candidate ingested via manual entry.2026-10-18
v1
No changelog recorded for this version.2026-07-30

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.

windows-rundll32-execution-with-uncommon-dll-cpl-inf-extension-in-command-line-c3a99af4

title: Windows rundll32 Process Creation With Uncommon DLL Extension in Command Line
id: 42c7c0ec-a67b-41b6-9821-15ff7be10150
status: test
description: This rule flags Windows process creation events where rundll32.exe is launched and the command line does not contain common file extensions commonly passed to rundll32 (e.g., .cpl, .dll, .inf), excluding specific known installer and update scenarios. Attackers may abuse rundll32 to load non-standard DLL or related files, blending execution into legitimate Windows tooling while evading expectations about typical extension usage. The detection relies on process creation telemetry including Image, OriginalFileName, ParentImage, and CommandLine content.
references:
  - https://twitter.com/mrd0x/status/1481630810495139841?s=12
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_creation/proc_creation_win_rundll32_uncommon_dll_extension.yml
author: Tim Shelton, Florian Roth (Nextron Systems), Yassine Oukessou, Huntrule Team
date: 2022-01-13
modified: 2026-10-13
tags:
  - attack.stealth
  - attack.t1218.011
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    - Image|endswith: \rundll32.exe
    - OriginalFileName: RUNDLL32.EXE
  filter_main_null:
    CommandLine: null
  filter_main_empty:
    CommandLine: ""
  filter_main_known_extension:
    - CommandLine|contains:
        - ".cpl "
        - .cpl,
        - .cpl"
        - .cpl'
        - ".dll "
        - .dll,
        - .dll"
        - .dll'
        - ".inf "
        - .inf,
        - .inf"
        - .inf'
    - CommandLine|endswith:
        - .cpl
        - .dll
        - ".inf"
  filter_main_localserver:
    CommandLine|contains: " -localserver "
  filter_main_zzzzInvokeManagedCustomActionOutOfProc:
    ParentImage|endswith: \msiexec.exe
    CommandLine|contains|all:
      - :\Windows\Installer\
      - .tmp
      - zzzzInvokeManagedCustomActionOutOfProc
  filter_main_streamci:
    Image: C:\Windows\System32\rundll32.exe
    ParentImage: C:\Windows\System32\svchost.exe
    CommandLine|contains: " streamci,StreamingDeviceSetup {"
  filter_optional_EdgeUpdate:
    ParentCommandLine|contains|all:
      - :\Users\
      - \AppData\Local\Microsoft\EdgeUpdate\Install\{
      - \EDGEMITMP_
      - .tmp\setup.exe
      - --install-archive=
      - --previous-version=
      - --msedgewebview --verbose-logging --do-not-launch-msedge --user-level
  condition: selection and not 1 of filter_main_* and not 1 of filter_optional_*
falsepositives:
  - Unknown
level: medium
regression_tests_path: regression_data/rules/windows/process_creation/proc_creation_win_rundll32_uncommon_dll_extension/info.yml
license: DRL-1.1
related:
  - id: c3a99af4-35a9-4668-879e-c09aeb4f2bdf
    type: derived

Convert

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