Potential Script Proxy Execution Via CL_Mutexverifiers.ps1 — Sigma Rule

Rule metadata and linked tags

Author: Nasreddine Bencherchali (Nextron Systems), oscd.community, Natalia Shornikova, frack113. Source status: test; severity: medium. Source dates: 2022-05-21 / 2023-08-17.

{
  "category": "process_creation",
  "product": "windows"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: e503018613d39b2bfa187d2050ac06715d81e435cb7075f6900a375c638ebde8

Detection logic

Original source YAML. Source-tag agreement is not proof of complete semantic coverage. This rule has not been compiled for a SIEM backend or validated against live telemetry here.

title: Potential Script Proxy Execution Via CL_Mutexverifiers.ps1
id: 1e0e1a81-e79b-44bc-935b-ddb9c8006b3d
status: test
description: Detects the use of the Microsoft signed script "CL_mutexverifiers" to proxy the execution of additional PowerShell script commands
references:
    - https://lolbas-project.github.io/lolbas/Scripts/CL_mutexverifiers/
author: Nasreddine Bencherchali (Nextron Systems), oscd.community, Natalia Shornikova, frack113
date: 2022-05-21
modified: 2023-08-17
tags:
    - attack.stealth
    - attack.t1216
logsource:
    category: process_creation
    product: windows
detection:
    selection_pwsh:
        ParentImage|endswith:
            # Note: to avoid potential FPs we assume the script was launched from powershell. But in theory it can be launched by any Powershell like process
            - '\powershell.exe'
            - '\pwsh.exe'
        Image|endswith: '\powershell.exe'
        CommandLine|contains: ' -nologo -windowstyle minimized -file '
    selection_temp:
        # Note: Since the function uses "env:temp" the value will change depending on the context of exec
        CommandLine|contains:
            - '\AppData\Local\Temp\'
            - '\Windows\Temp\'
    condition: all of selection_*
falsepositives:
    - Unknown
level: medium

Original YAML and metadata in JSON

False positives

• Unknown

Source references

• https://lolbas-project.github.io/lolbas/Scripts/CL_mutexverifiers/