Wlrmdr.EXE Uncommon Argument Or Child Process — Sigma Rule

{
  "category": "process_creation",
  "product": "windows"
}

title: Wlrmdr.EXE Uncommon Argument Or Child Process
id: 9cfc00b6-bfb7-49ce-9781-ef78503154bb
status: experimental
description: |
    Detects the execution of "Wlrmdr.exe" with the "-u" command line flag which allows anything passed to it to be an argument of the ShellExecute API, which would allow an attacker to execute arbitrary binaries.
    This detection also focuses on any uncommon child processes spawned from "Wlrmdr.exe" as a supplement for those that posses "ParentImage" telemetry.
references:
    - https://twitter.com/0gtweet/status/1493963591745220608?s=20&t=xUg9DsZhJy1q9bPTUWgeIQ
    - https://lolbas-project.github.io/lolbas/Binaries/Wlrmdr/
author: frack113, manasmbellani
date: 2022-02-16
modified: 2025-10-31
tags:
    - attack.stealth
    - attack.t1218
logsource:
    category: process_creation
    product: windows
detection:
    selection_parent: # This selection is looking for processes spawned from wlrmdr using the "-u" flag
        ParentImage|endswith: '\wlrmdr.exe'
    selection_child_img:
        - Image|endswith: '\wlrmdr.exe'
        - OriginalFileName: 'WLRMNDR.EXE'
    selection_child_cli_flags_s:
        CommandLine|contains|windash: '-s '
    selection_child_cli_flags_f:
        CommandLine|contains|windash: '-f '
    selection_child_cli_flags_t:
        CommandLine|contains|windash: '-t '
    selection_child_cli_flags_m:
        CommandLine|contains|windash: '-m '
    selection_child_cli_flags_a:
        CommandLine|contains|windash: '-a '
    selection_child_cli_flags_u:
        CommandLine|contains|windash: '-u '
    filter_main_winlogon:
        ParentImage: 'C:\Windows\System32\winlogon.exe'
    filter_main_empty:
        ParentImage:
            - ''
            - '-'
    filter_main_null:
        ParentImage: null
    condition: selection_parent or (all of selection_child_* and not 1 of filter_main_*)
falsepositives:
    - Unknown
level: medium