sigmamediumHunting

WSL Child Process Anomaly

Detects uncommon or suspicious child processes spawning from a WSL process. This could indicate an attempt to evade parent/child relationship detections or persistence attempts via cron using WSL

MITRE ATT&CK

T1218 T1202

executiondefense-evasion

Detection Query

selection_parent:
  ParentImage|endswith:
    - \wsl.exe
    - \wslhost.exe
selection_children_images:
  Image|endswith:
    - \calc.exe
    - \cmd.exe
    - \cscript.exe
    - \mshta.exe
    - \powershell.exe
    - \pwsh.exe
    - \regsvr32.exe
    - \rundll32.exe
    - \wscript.exe
selection_children_paths:
  Image|contains:
    - \AppData\Local\Temp\
    - C:\Users\Public\
    - C:\Windows\Temp\
    - C:\Temp\
    - \Downloads\
    - \Desktop\
condition: selection_parent and 1 of selection_children_*

Author

Nasreddine Bencherchali (Nextron Systems)

Created

2023-01-23

Data Sources

windowsProcess Creation Events

Platforms

windows

References

Tags

attack.executionattack.defense-evasionattack.t1218attack.t1202

Raw Content

title: WSL Child Process Anomaly
id: 2267fe65-0681-42ad-9a6d-46553d3f3480
related:
    - id: dec44ca7-61ad-493c-bfd7-8819c5faa09b # LOLBIN Rule
      type: derived
status: test
description: Detects uncommon or suspicious child processes spawning from a WSL process. This could indicate an attempt to evade parent/child relationship detections or persistence attempts via cron using WSL
references:
    - https://lolbas-project.github.io/lolbas/OtherMSBinaries/Wsl/
    - https://twitter.com/nas_bench/status/1535431474429808642
author: Nasreddine Bencherchali (Nextron Systems)
date: 2023-01-23
modified: 2023-08-15
tags:
    - attack.execution
    - attack.defense-evasion
    - attack.t1218
    - attack.t1202
logsource:
    category: process_creation
    product: windows
detection:
    selection_parent:
        ParentImage|endswith:
            - '\wsl.exe'
            - '\wslhost.exe'
    selection_children_images:
        Image|endswith:
            # Add more suspicious/uncommon "lolbin" processes
            - '\calc.exe'
            - '\cmd.exe'
            - '\cscript.exe'
            - '\mshta.exe'
            - '\powershell.exe'
            - '\pwsh.exe'
            - '\regsvr32.exe'
            - '\rundll32.exe'
            - '\wscript.exe'
    selection_children_paths:
        Image|contains:
            - '\AppData\Local\Temp\'
            - 'C:\Users\Public\'
            - 'C:\Windows\Temp\'
            - 'C:\Temp\'
            - '\Downloads\'
            - '\Desktop\'
    condition: selection_parent and 1 of selection_children_*
falsepositives:
    - Unknown
level: medium