Windows: Suspicious CustomShellHost.exe execution spawned by non-Explorer parent

Alerts on CustomShellHost.exe executions where explorer.exe is not the expected parent process image.

FreeReviewedSigma · High · v2

Product: windows
Category: process_creation
Author: Nasreddine Bencherchali (Nextron Systems) (SigmaHQ), DRL 1.1
Published: 2022-08-19
Updated: 2026-07-31

ATT&CK techniques

Defense Evasion

Recon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
- T1216System Script Proxy Execution
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule flags process creation events where the parent process image ends with \CustomShellHost.exe, but the corresponding child process is not located under C:\Windows\explorer.exe. CustomShellHost is a signed Windows binary that attackers may misuse to reduce visibility and evade defenses. The detection relies on Windows process creation telemetry, specifically the parent image path ending pattern and the child image path matching explorer.exe.

Reporting behind it

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Windows: Uncommon Child Processes Spawned by sigverif.exe

PowerShell: Signed UtilityFunctions.ps1 Loading Managed DLL via Proxy Execution

Windows PowerShell Script Proxy Execution via CL_mutexverifiers.ps1

PowerShell Assembly Loading via CL_LoadAssembly.ps1 Functions

Windows: Suspicious CustomShellHost.exe execution spawned by non-Explorer parent

Pivot detection · T1216 · 9 related

Changelog

v2
Candidate ingested via manual entry.2026-07-31
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-suspicious-customshellhost-exe-execution-from-non-explorer-parent-84b14121

title: "Windows: Suspicious CustomShellHost.exe execution spawned by non-Explorer parent"
id: 38e0e9e8-222f-48ba-b0d1-741c22e8a00a
status: test
description: This rule flags process creation events where the parent process image ends with \CustomShellHost.exe, but the corresponding child process is not located under C:\Windows\explorer.exe. CustomShellHost is a signed Windows binary that attackers may misuse to reduce visibility and evade defenses. The detection relies on Windows process creation telemetry, specifically the parent image path ending pattern and the child image path matching explorer.exe.
references:
  - https://github.com/LOLBAS-Project/LOLBAS/pull/180
  - https://lolbas-project.github.io/lolbas/Binaries/CustomShellHost/
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_creation/proc_creation_win_customshellhost_susp_exec.yml
author: Nasreddine Bencherchali (Nextron Systems), Huntrule Team
date: 2022-08-19
modified: 2025-10-29
tags:
  - attack.stealth
  - attack.t1216
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    ParentImage|endswith: \CustomShellHost.exe
  filter_main_explorer:
    Image: C:\Windows\explorer.exe
  condition: selection and not 1 of filter_main_*
falsepositives:
  - False positives are unlikely, investigate matches carefully.
level: high
license: DRL-1.1
related:
  - id: 84b14121-9d14-416e-800b-f3b829c5a14d
    type: derived

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