Suspicious CustomShellHost Execution

Status: test
Severity: high
Log source: category process_creation, product windows
Author: Nasreddine Bencherchali (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects the execution of CustomShellHost.exe where the child isn't located in 'C:\Windows\explorer.exe'. CustomShellHost is a known LOLBin that can be abused by attackers for defense evasion techniques.

Known false positives

False positives are unlikely, investigate matches carefully.

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1216` System Script Proxy Execution

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation
Security-Auditing	Event ID 4688: A new process has been created.

Rule body

title: Suspicious CustomShellHost Execution
id: 84b14121-9d14-416e-800b-f3b829c5a14d
status: test
description: |
    Detects the execution of CustomShellHost.exe where the child isn't located in 'C:\Windows\explorer.exe'. CustomShellHost is a known LOLBin that can be abused by attackers for defense evasion techniques.
references:
    - https://github.com/LOLBAS-Project/LOLBAS/pull/180
    - https://lolbas-project.github.io/lolbas/Binaries/CustomShellHost/
author: Nasreddine Bencherchali (Nextron Systems)
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

Stages and Predicates

Stage 0: `condition`

selection and not 1 of filter_main_*

Stage 1: `selection`

selection:
    ParentImage|endswith: '\CustomShellHost.exe'

Stage 2: `not filter_main_explorer`

filter_main_explorer:
    Image: 'C:\Windows\explorer.exe'

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`Image`	eq	`C:\Windows\explorer.exe`	`excludes:Image` `field:"Image" value:"C:\Windows\explorer.exe"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`ParentImage`	ends_with	`\CustomShellHost.exe`	`field:"ParentImage" kind:ends_with value:"\CustomShellHost.exe"`