Windows Process Creation: Default-Argument Invocation of Rundll32/WerFault/Regsvcs/Regasm/Regsvr32

Alerts on suspicious Windows process launches of key binaries with missing/empty arguments, excluding common Edge/Chromium installer use.

FreeReviewedSigma · High · v1

Product: windows
Category: process_creation
Author: Oleg Kolesnikov @securonix invrep_de, oscd.community, Florian Roth (Nextron Systems), Christian Burkard (Nextron Systems) (SigmaHQ), DRL 1.1
Published: 2020-10-23
Updated: 2026-07-30

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 executions where the Image and CommandLine end with specific binaries (rundll32.exe, WerFault.exe, regsvcs.exe, regasm.exe, or regsvr32.exe) without including additional command-line arguments. Attackers may rely on these “default” or improperly handled invocations as sacrificial processes to carry out capability injection or other stealthy actions without conforming to normal execution patterns. The detection relies on process creation telemetry that captures the executable path and full command line, with exclusions for certain EdgeUpdate/Chromium uninstall-related rundll32.exe activity.

Reporting behind it

Related detections9 linkedT1218.011 — drag to rearrange

Malicious DLL Execution With Non Standard Extension via rundll32

Andromeda Loader Execution via Rundll32 Desktop.ini Ordinal

Suspicious rundll32 Execution of sqlite3 DLL by Ordinal with TLB Argument

Malicious Zardoor Backdoor Execution via rundll32 (via process_creation)

Malicious Rundll32 Loading an Export From a User Path (via process_creation)

Renamed Regsvr32 or Rundll32 Loading a DLL With a Non-Standard Extension (via process_creation)

Malicious Rundll32 DllRegisterServer Execution From a User-Writable Path (via process_creation)

IMEEX Framework DLL Execution via Rundll32 Loading imaadp (via process_creation)

Suspicious Persistence via pcalua Launching rundll32 Control_RunDLL

Windows Process Creation: Default-Argument Invocation of Rundll32/WerFault/Regsvcs/Regasm/Regsvr32

Pivot detection · T1218.011 · 9 related

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

windows-process-creation-default-argument-invocation-of-rundll32-werfault-regsvc-a7c3d773

title: "Windows Process Creation: Default-Argument Invocation of Rundll32/WerFault/Regsvcs/Regasm/Regsvr32"
id: d969f74f-c1ac-4e5e-8a12-3e8cf1668db1
related:
  - id: f5647edc-a7bf-4737-ab50-ef8c60dc3add
    type: obsolete
  - id: a7c3d773-caef-227e-a7e7-c2f13c622329
    type: derived
status: test
description: This rule flags Windows process executions where the Image and CommandLine end with specific binaries (rundll32.exe, WerFault.exe, regsvcs.exe, regasm.exe, or regsvr32.exe) without including additional command-line arguments. Attackers may rely on these “default” or improperly handled invocations as sacrificial processes to carry out capability injection or other stealthy actions without conforming to normal execution patterns. The detection relies on process creation telemetry that captures the executable path and full command line, with exclusions for certain EdgeUpdate/Chromium uninstall-related rundll32.exe activity.
references:
  - https://blog.malwarebytes.com/malwarebytes-news/2020/10/kraken-attack-abuses-wer-service/
  - https://www.cobaltstrike.com/help-opsec
  - https://twitter.com/CyberRaiju/status/1251492025678983169
  - https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/regsvr32
  - https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/rundll32
  - https://learn.microsoft.com/en-us/dotnet/framework/tools/regasm-exe-assembly-registration-tool
  - https://learn.microsoft.com/en-us/dotnet/framework/tools/regsvcs-exe-net-services-installation-tool
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_creation/proc_creation_win_susp_bad_opsec_sacrificial_processes.yml
author: Oleg Kolesnikov @securonix invrep_de, oscd.community, Florian Roth (Nextron Systems), Christian Burkard (Nextron Systems), Huntrule Team
date: 2020-10-23
modified: 2024-08-15
tags:
  - attack.stealth
  - attack.t1218.011
logsource:
  category: process_creation
  product: windows
detection:
  selection_werfault:
    Image|endswith: \WerFault.exe
    CommandLine|endswith: WerFault.exe
  selection_rundll32:
    Image|endswith: \rundll32.exe
    CommandLine|endswith: rundll32.exe
  selection_regsvcs:
    Image|endswith: \regsvcs.exe
    CommandLine|endswith: regsvcs.exe
  selection_regasm:
    Image|endswith: \regasm.exe
    CommandLine|endswith: regasm.exe
  selection_regsvr32:
    Image|endswith: \regsvr32.exe
    CommandLine|endswith: regsvr32.exe
  filter_optional_edge_update:
    ParentImage|contains: \AppData\Local\Microsoft\EdgeUpdate\Install\{
    Image|endswith: \rundll32.exe
    CommandLine|endswith: rundll32.exe
  filter_optional_chromium_installer:
    ParentImage|contains:
      - \AppData\Local\BraveSoftware\Brave-Browser\Application\
      - \AppData\Local\Google\Chrome\Application\
    ParentImage|endswith: \Installer\setup.exe
    ParentCommandLine|contains: "--uninstall "
    Image|endswith: \rundll32.exe
    CommandLine|endswith: rundll32.exe
  condition: 1 of selection_* and not 1 of filter_optional_*
falsepositives:
  - Unlikely
level: high
license: DRL-1.1

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