Execute Code with Pester.bat as Parent

Status: test
Severity: medium
Log source: category process_creation, product windows
Author: frack113, Nasreddine Bencherchali
Source: github.com/SigmaHQ/sigma

Detects code execution via Pester.bat (Pester - Powershell Modulte for testing)

Known false positives

Legitimate use of Pester for writing tests for Powershell scripts and modules

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1059.001` Command and Scripting Interpreter: PowerShell
Stealth	`T1216` System Script Proxy Execution

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation

Rule body

title: Execute Code with Pester.bat as Parent
id: 18988e1b-9087-4f8a-82fe-0414dce49878
related:
    - id: 59e938ff-0d6d-4dc3-b13f-36cc28734d4e
      type: similar
status: test
description: Detects code execution via Pester.bat (Pester - Powershell Modulte for testing)
references:
    - https://twitter.com/Oddvarmoe/status/993383596244258816
    - https://twitter.com/_st0pp3r_/status/1560072680887525378
author: frack113, Nasreddine Bencherchali
date: 2022-08-20
tags:
    - attack.execution
    - attack.stealth
    - attack.t1059.001
    - attack.t1216
logsource:
    category: process_creation
    product: windows
detection:
    selection_module:
        ParentImage|endswith:
            - '\powershell.exe'
            - '\pwsh.exe'
        ParentCommandLine|contains: '\WindowsPowerShell\Modules\Pester\'
    selection_cli:
        ParentCommandLine|contains:
            - '{ Invoke-Pester -EnableExit ;'
            - '{ Get-Help "'
    condition: all of selection_*
falsepositives:
    - Legitimate use of Pester for writing tests for Powershell scripts and modules
level: medium

Stages and Predicates

Stage 0: `condition`

all of selection_*

Stage 1: `selection_module`

selection_module:
    ParentImage|endswith:
        - '\powershell.exe'
        - '\pwsh.exe'
    ParentCommandLine|contains: '\WindowsPowerShell\Modules\Pester\'

Stage 2: `selection_cli`

selection_cli:
    ParentCommandLine|contains:
        - '{ Invoke-Pester -EnableExit ;'
        - '{ Get-Help "'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`ParentCommandLine`	match	`\WindowsPowerShell\Modules\Pester\` `{ Get-Help "` `{ Invoke-Pester -EnableExit ;`	`field:"ParentCommandLine" kind:match`
`ParentImage`	ends_with	`\powershell.exe` corpus 24 (sigma 24) `\pwsh.exe` corpus 21 (sigma 21)	`field:"ParentImage" kind:ends_with`

Execute Code with Pester.bat as Parent

Known false positives

MITRE ATT&CK coverage

Telemetry coverage

Rule body

Stages and Predicates

Stage 0: condition

Stage 1: selection_module

Stage 2: selection_cli

Indicators

Stage 0: `condition`

Stage 1: `selection_module`

Stage 2: `selection_cli`