Windows: rundll32.exe spawning explorer.exe child process (shell32.Control_RunDLL)

Alerts on rundll32.exe spawning explorer.exe, an uncommon child process pattern that may indicate stealthy execution via shell components.

FreeUnreviewedSigmahighv1

windows-rundll32-exe-spawning-explorer-exe-child-process-shell32-control-rundll-caa06de8

title: "Windows: rundll32.exe spawning explorer.exe child process (shell32.Control_RunDLL)"
id: b4e4ed84-8c82-445f-bd15-726a42e3bf19
status: test
description: This rule flags executions where rundll32.exe spawns explorer.exe as a child process. Such a process tree is uncommon and can indicate attempts to launch a user-facing interface or mask execution through Windows shell components. It relies on process creation telemetry, matching on parent process image ending in rundll32.exe and child process image ending in explorer.exe, while excluding cases where the parent command line contains the specific shell32.dll Control_RunDLL string.
references:
  - https://redcanary.com/blog/intelligence-insights-november-2021/
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_creation/proc_creation_win_rundll32_spawn_explorer.yml
author: elhoim, CD_ROM_, Huntrule Team
date: 2022-04-27
modified: 2022-05-25
tags:
  - attack.stealth
  - attack.t1218.011
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    ParentImage|endswith: \rundll32.exe
    Image|endswith: \explorer.exe
  filter:
    ParentCommandLine|contains: \shell32.dll,Control_RunDLL
  condition: selection and not filter
falsepositives:
  - Unknown
level: high
license: DRL-1.1
related:
  - id: caa06de8-fdef-4c91-826a-7f9e163eef4b
    type: derived

What it detects

This rule flags executions where rundll32.exe spawns explorer.exe as a child process. Such a process tree is uncommon and can indicate attempts to launch a user-facing interface or mask execution through Windows shell components. It relies on process creation telemetry, matching on parent process image ending in rundll32.exe and child process image ending in explorer.exe, while excluding cases where the parent command line contains the specific shell32.dll Control_RunDLL string.

Known false positives

Unknown

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