Add Windows Capability Via PowerShell Cmdlet

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

Detects usage of the "Add-WindowsCapability" cmdlet to add Windows capabilities. Notable capabilities could be "OpenSSH" and others.

Known false positives

Legitimate usage of the capabilities by administrators or users. Add additional filters accordingly.

MITRE ATT&CK coverage

Tactic	Techniques
Execution	No specific technique

Telemetry coverage

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

Rule body

title: Add Windows Capability Via PowerShell Cmdlet
id: b36d01a3-ddaf-4804-be18-18a6247adfcd
related:
    - id: 155c7fd5-47b4-49b2-bbeb-eb4fab335429
      type: similar
status: test
description: Detects usage of the "Add-WindowsCapability" cmdlet to add Windows capabilities. Notable capabilities could be "OpenSSH" and others.
references:
    - https://learn.microsoft.com/en-us/windows-server/administration/openssh/openssh_install_firstuse?tabs=powershell
    - https://www.virustotal.com/gui/file/af1c82237b6e5a3a7cdbad82cc498d298c67845d92971bada450023d1335e267/content
author: Nasreddine Bencherchali (Nextron Systems)
date: 2023-01-22
modified: 2023-05-09
tags:
    - attack.execution
logsource:
    product: windows
    category: process_creation
detection:
    selection_img:
        - Image|endswith:
              - '\powershell.exe'
              - '\pwsh.exe'
        - OriginalFileName:
              - 'PowerShell.EXE'
              - 'pwsh.dll'
    selection_cmdlet:
        CommandLine|contains: 'Add-WindowsCapability'
    selection_capa:
        CommandLine|contains: 'OpenSSH.' # For both "OpenSSH.Server" and "OpenSSH.Client"
    condition: all of selection_*
falsepositives:
    - Legitimate usage of the capabilities by administrators or users. Add additional filters accordingly.
level: medium

Stages and Predicates

Stage 0: `condition`

all of selection_*

Stage 1: `selection_img`

selection_img:
    - Image|endswith:
          - '\powershell.exe'
          - '\pwsh.exe'
    - OriginalFileName:
          - 'PowerShell.EXE'
          - 'pwsh.dll'

Stage 2: `selection_cmdlet`

selection_cmdlet:
    CommandLine|contains: 'Add-WindowsCapability'

Stage 3: `selection_capa`

selection_capa:
    CommandLine|contains: 'OpenSSH.'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	match	`Add-WindowsCapability` `OpenSSH.`	`field:"CommandLine" kind:match`
`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`

Add Windows Capability Via PowerShell Cmdlet

Known false positives

MITRE ATT&CK coverage

Telemetry coverage

Rule body

Stages and Predicates

Stage 0: condition

Stage 1: selection_img

Stage 2: selection_cmdlet

Stage 3: selection_capa

Indicators

Stage 0: `condition`

Stage 1: `selection_img`

Stage 2: `selection_cmdlet`

Stage 3: `selection_capa`