Arbitrary Command Execution Using WSL

title: Arbitrary Command Execution Using WSL
id: dec44ca7-61ad-493c-bfd7-8819c5faa09b
related:
    - id: 2267fe65-0681-42ad-9a6d-46553d3f3480 # Generic susp child processes rules
      type: similar
status: test
description: |
    Detects potential abuse of Windows Subsystem for Linux (WSL) binary as a Living of the Land binary in order to execute arbitrary Linux or Windows commands.
references:
    - https://lolbas-project.github.io/lolbas/OtherMSBinaries/Wsl/
    - https://twitter.com/nas_bench/status/1535431474429808642
author: oscd.community, Zach Stanford @svch0st, Nasreddine Bencherchali (Nextron Systems)
date: 2020-10-05
modified: 2023-04-12
tags:
    - attack.execution
    - attack.stealth
    - attack.t1218
    - attack.t1202
    - detection.threat-hunting
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith: '\wsl.exe'
        - OriginalFileName: 'wsl.exe'
    selection_cli:
        CommandLine|contains:
            - ' -e '
            - ' --exec'
            - ' --system'
            - ' --shell-type '
            - ' /mnt/c' # Path to mounted "C:\" partition (Indication of running Windows binaries via WSL)
            - ' --user root'
            - ' -u root'
            - '--debug-shell'
    filter_main_kill:
        # This filter is to handle a FP that occurs when a process is spawned from WSL and then closed by the user
        # Example would be to open VsCode through it's server extension from WSL
            # GrandparentCommandLine: "C:\Users\XXX\AppData\Local\Programs\Microsoft VS Code\Code.exe" --ms-enable-electron-run-as-node c:\Users\XXX\.vscode\extensions\ms-vscode-remote.remote-wsl-0.72.0\dist\wslDaemon.js
            # ParentCommandLine: C:\WINDOWS\system32\cmd.exe /d /s /c "C:\WINDOWS\System32\wsl.exe -d Ubuntu-20.04 -e kill 1366"
            # CommandLine: C:\WINDOWS\System32\wsl.exe -d Ubuntu-20.04 -e kill 1366
        ParentImage|endswith: '\cmd.exe'
        CommandLine|contains|all:
            - ' -d '
            - ' -e kill '
    condition: all of selection_* and not 1 of filter_main_*
falsepositives:
    - Automation and orchestration scripts may use this method to execute scripts etc.
    - Legitimate use by Windows to kill processes opened via WSL (example VsCode WSL server)
level: medium