Unusually Long PowerShell CommandLine

Status: test
Severity: low
Log source: category process_creation, product windows
Author: oscd.community, Natalia Shornikova
Source: github.com/SigmaHQ/sigma

Detects unusually long PowerShell command lines with a length of 1000 characters or more

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1059.001` Command and Scripting Interpreter: PowerShell

Telemetry coverage

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

Rule body

title: Unusually Long PowerShell CommandLine
id: d0d28567-4b9a-45e2-8bbc-fb1b66a1f7f6
status: test
description: Detects unusually long PowerShell command lines with a length of 1000 characters or more
references:
    - https://speakerdeck.com/heirhabarov/hunting-for-powershell-abuse
author: oscd.community, Natalia Shornikova
date: 2020-10-06
modified: 2023-04-14
tags:
    - attack.execution
    - attack.t1059.001
    - detection.threat-hunting
logsource:
    category: process_creation
    product: windows
detection:
    selection_powershell:
        - Image|endswith:
              - '\powershell.exe'
              - '\pwsh.exe'
        - OriginalFileName:
              - 'PowerShell.EXE'
              - 'pwsh.dll'
        - Description: 'Windows Powershell'
        - Product: 'PowerShell Core 6'
    selection_length:
        CommandLine|re: '.{1000,}'
    condition: all of selection_*
falsepositives:
    - Unknown
level: low

Stages and Predicates

Stage 0: `condition`

all of selection_*

Stage 1: `selection_powershell`

selection_powershell:
    - Image|endswith:
          - '\powershell.exe'
          - '\pwsh.exe'
    - OriginalFileName:
          - 'PowerShell.EXE'
          - 'pwsh.dll'
    - Description: 'Windows Powershell'
    - Product: 'PowerShell Core 6'

Stage 2: `selection_length`

selection_length:
    CommandLine|re: '.{1000,}'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	regex_match	`.{1000,}`	`field:"CommandLine" kind:regex_match value:".{1000,}"`
`Description`	eq	`Windows Powershell` corpus 3 (sigma 3)	`field:"Description" kind:eq value:"Windows Powershell"`
`Image`	ends_with	`\powershell.exe` corpus 179 (sigma 178, kusto 1) `\pwsh.exe` corpus 165 (sigma 164, kusto 1)	`field:"Image" kind:ends_with`
`OriginalFileName`	eq	`PowerShell.EXE` corpus 138 (sigma 84, splunk 30, elastic 24) `pwsh.dll` corpus 112 (sigma 79, splunk 30, elastic 3)	`field:"OriginalFileName" kind:eq`
`Product`	eq	`PowerShell Core 6` corpus 3 (sigma 3)	`field:"Product" kind:eq value:"PowerShell Core 6"`

Unusually Long PowerShell CommandLine

MITRE ATT&CK coverage

Telemetry coverage

Rule body

Stages and Predicates

Stage 0: condition

Stage 1: selection_powershell

Stage 2: selection_length

Indicators

Stage 0: `condition`

Stage 1: `selection_powershell`

Stage 2: `selection_length`