Sigma rule: Suspicious Workstation Locking via Rundll32

A detection rule from the SigmaHQ repository, shown as its author published it. Dataset version ref-5f95b558d0a3, updated 2023-02-09T00:00:00.000Z.

Rule

Title
Suspicious Workstation Locking via Rundll32
Status
test
Level
medium
Author
frack113
Date
2022-06-04
Modified
2023-02-09
File
rules/windows/process_creation/proc_creation_win_rundll32_user32_dll.yml
Commit
ccbb0369507f796db0b0ae6854c8a2be471b9d84

Detects a suspicious call to the user32.dll function that locks the user workstation

Log source

product
windows
category
process_creation

Detection

selection_call_img:
    - Image|endswith: '\rundll32.exe'
    - OriginalFileName: 'RUNDLL32.EXE'
selection_call_parent:
    ParentImage|endswith: '\cmd.exe'
selection_call_cli:
    CommandLine|contains: 'user32.dll,'
selection_function:
    CommandLine|contains: 'LockWorkStation'
condition: all of selection_*

False positives (as the rule lists them)

  • Scripts or links on the user desktop used to lock the workstation instead of Windows+L or the menu option

Tags

  • attack.stealth

References

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_rundll32_user32_dll.yml

Sources and licences

  • SigmaHQ

    "Suspicious Workstation Locking via Rundll32" by frack113 (SigmaHQ). Rule: https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules/windows/process_creation/proc_creation_win_rundll32_user32_dll.yml.
    Licensed under the Detection Rule License (DRL) 1.1: https://github.com/SigmaHQ/Detection-Rule-License

    Detection Rule License (DRL) 1.1

Cite this page

Dragons Eye Ransomware Tracker, "Sigma rule: Suspicious Workstation Locking via Rundll32",
entity page, dataset version ref-5f95b558d0a3, updated 2023-02-09T00:00:00.000Z,
https://ransomware-tracker.com/detections/sigma/3b5b0213-0460-4e3f-8937-3abf98ff7dcc (accessed 2026-11-03).
Underlying source: SigmaHQ rule 3b5b0213-0460-4e3f-8937-3abf98ff7dcc, commit ccbb0369507f796db0b0ae6854c8a2be471b9d84.

Pages change. The dataset version identifies the data, but no archive of old versions is kept, so this citation cannot be replayed later.