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Detection rules › Sigma

Potential Script Proxy Execution Via CL_Mutexverifiers.ps1

Status
test
Severity
medium
Log source
product windows, category process_creation
Author
Nasreddine Bencherchali (Nextron Systems), oscd.community, Natalia Shornikova, frack113
Source
github.com/SigmaHQ/sigma

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

MITRE ATT&CK coverage

TacticTechniques
StealthT1216 System Script Proxy Execution

Event coverage

ProviderEventTitle
SysmonEvent ID 1Process creation
Security-AuditingEvent ID 4688A new process has been created.

Rule body yaml

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

Stages and Predicates

Stage 0: condition

all of selection_*

Stage 1: selection_pwsh

selection_pwsh:
    ParentImage|endswith:
        - '\powershell.exe'
        - '\pwsh.exe'
    Image|endswith: '\powershell.exe'
    CommandLine|contains: ' -nologo -windowstyle minimized -file '

Stage 2: selection_temp

selection_temp:
    CommandLine|contains:
        - '\AppData\Local\Temp\'
        - '\Windows\Temp\'

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

FieldKindValues
CommandLinematch
  • -nologo -windowstyle minimized -file
  • \AppData\Local\Temp\ corpus 26 (sigma 26)
  • \Windows\Temp\ corpus 12 (sigma 12)
Imageends_with
  • \powershell.exe corpus 182 (sigma 182)
ParentImageends_with
  • \powershell.exe corpus 24 (sigma 24)
  • \pwsh.exe corpus 21 (sigma 21)