Windows: Suspicious userinit.exe Child Process Creation

Alerts when userinit.exe spawns an atypical child process, excluding known benign explorer and netlogon command-line patterns.

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windows-suspicious-userinit-exe-child-process-creation-b655a06a

title: "Windows: Suspicious userinit.exe Child Process Creation"
id: 15f96542-2db7-48ff-b4d1-cffd908265c2
status: test
description: This rule flags process creation events where the parent process is userinit.exe and the child process command line does not match common benign patterns. Attackers may abuse userinit to spawn unexpected processes for privilege escalation or stealthy execution during user logon. It relies on Windows process creation telemetry, including parent image path and child command-line content, to identify unusual child process relationships.
references:
  - https://twitter.com/SBousseaden/status/1139811587760562176
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_creation/proc_creation_win_susp_userinit_child.yml
author: Florian Roth (Nextron Systems), Samir Bousseaden (idea), Huntrule Team
date: 2019-06-17
modified: 2025-10-17
tags:
  - attack.privilege-escalation
  - attack.stealth
  - attack.t1055
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    ParentImage|endswith: \userinit.exe
  filter_main_netlogon:
    CommandLine|contains: \netlogon\
  filter_main_explorer:
    - Image|endswith: \explorer.exe
    - OriginalFileName: explorer.exe
    - CommandLine: C:\Windows\Explorer.EXE
  filter_main_null:
    Image: null
  condition: selection and not 1 of filter_main_*
falsepositives:
  - Administrative scripts
level: medium
license: DRL-1.1
related:
  - id: b655a06a-31c0-477a-95c2-3726b83d649d
    type: derived

What it detects

This rule flags process creation events where the parent process is userinit.exe and the child process command line does not match common benign patterns. Attackers may abuse userinit to spawn unexpected processes for privilege escalation or stealthy execution during user logon. It relies on Windows process creation telemetry, including parent image path and child command-line content, to identify unusual child process relationships.

Known false positives

Administrative scripts

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