Potential Script Proxy Execution Via CL_Mutexverifiers.ps1

Hunt Hypothesis

Detects the use of the Microsoft signed script “CL_mutexverifiers” to proxy the execution of additional PowerShell script commands

Detection Rule

Sigma (Original)

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

KQL (Azure Sentinel)

imProcessCreate
| where (((ParentProcessName endswith "\\powershell.exe" or ParentProcessName endswith "\\pwsh.exe") or (ActingProcessName endswith "\\powershell.exe" or ActingProcessName endswith "\\pwsh.exe")) and TargetProcessName endswith "\\powershell.exe" and TargetProcessCommandLine contains " -nologo -windowstyle minimized -file ") and (TargetProcessCommandLine contains "\\AppData\\Local\\Temp\\" or TargetProcessCommandLine contains "\\Windows\\Temp\\")

Required Data Sources

False Positive Guidance

• Unknown

MITRE ATT&CK Context

• Technique: T1216 — T1216

References

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