Sigma rule: Suspicious WSL Binary Hijack via Proxy Execution

Rule

Title

Suspicious WSL Binary Hijack via Proxy Execution

Status

experimental

Level

high

Author

Swachchhanda Shrawan Poudel (Nextron Systems)

Date

2026-05-05

File

rules/windows/process_creation/proc_creation_win_wsl_binary_hijack_execution.yml

Commit

ccbb0369507f796db0b0ae6854c8a2be471b9d84

Detects C:\Windows\System32\wsl.exe spawning a child wsl.exe process from outside the legitimate WSL install locations.
When WSL or bash is invoked, the System32 stub (wsl.exe) looks up the InstallLocation registry key and executes the wsl.exe found there.
An attacker who modifies InstallLocation to a controlled path causes the stub to transparently proxy execution to a malicious payload,
which then appears as a wsl.exe child of the legitimate System32 stub.

Log source

product

windows

category

process_creation

Detection

selection:
    ParentImage: 'C:\Windows\System32\wsl.exe'
    Image|endswith: '\wsl.exe'
filter_main_legit_paths_1:
    Image:
        - 'C:\Windows\System32\wsl.exe'
        - 'C:\Program Files\WSL\wsl.exe'
filter_main_legit_paths_2:
    Image|startswith:
        - 'C:\Windows\WinSxS\amd64_microsoft-windows-lxss-wsl_'
        - 'C:\Windows\WinSxS\arm64_microsoft-windows-lxss-wsl_'
        - 'C:\Program Files\WindowsApps\MicrosoftCorporationII.WindowsSubsystemForLinux'
filter_main_legit_paths_3:
    Image|startswith: 'C:\Users\'
    Image|contains: '\AppData\Local\Microsoft\WindowsApps\'
condition: selection and not 1 of filter_main_*

False positives (as the rule lists them)

• Unlikely

Tags

• attack.stealth
• attack.t1036.005
• attack.t1218

MITRE ATT&CK ids this rule names

• T1036.005
• T1218

References

• https://cardinalops.com/blog/bash-and-switch-hijacking-via-windows-subsystem-for-linux/
• https://blog.qualys.com/vulnerabilities-threat-research/2022/04/20/implications-of-windows-subsystem-for-linux-for-adversaries-defenders-part-2
• https://www.bleepingcomputer.com/news/security/new-malware-uses-windows-subsystem-for-linux-for-stealthy-attacks/
• https://thehackernews.com/2021/09/new-malware-targets-windows-subsystem.html
• https://learn.microsoft.com/en-us/windows/wsl/

Read on 2026-11-03T00:58:21.399Z under licence sigma-drl-1.1@d5f4c36a from https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules/windows/process_creation/proc_creation_win_wsl_binary_hijack_execution.yml