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

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