Rundll32 Execution With Unusual DLL Extension (via process_creation)

title: Rundll32 Execution With Unusual DLL Extension (via process_creation)
id: ac368b1d-91cf-59cc-9ae6-46152012d073
status: stable
description: This rule detects the execution of rundll32 with a command line that doesn't contain a common extension
references:
    - https://attack.mitre.org/techniques/T1218/011/
    - https://twitter.com/mrd0x/status/1481630810495139841?s=12
author: Huntrule Team
date: 2026-03-14
tags:
    - attack.stealth
    - attack.t1218.011
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        - Image|endswith: '\rundll32.exe'
        - OriginalFileName: 'RUNDLL32.EXE'
    filter_main_null:
        CommandLine:
    filter_main_empty:
        CommandLine: ''
    filter_main_known_extension:
        - CommandLine|contains:
              - '.cpl '
              - '.cpl,'
              - '.cpl"'
              - ".cpl'"
              - '.dll '
              - '.dll,'
              - '.dll"'
              - ".dll'"
              - '.inf '
              - '.inf,'
              - '.inf"'
              - ".inf'"
        - CommandLine|endswith:
              - '.cpl'
              - '.dll'
              - '.inf'
    filter_main_localserver:
        CommandLine|contains: ' -localserver '
    filter_main_zzzzInvokeManagedCustomActionOutOfProc:
        ParentImage|endswith: '\msiexec.exe'
        CommandLine|contains|all:
            - ':\Windows\Installer\'
            - '.tmp'
            - 'zzzzInvokeManagedCustomActionOutOfProc'
    filter_optional_EdgeUpdate:
        ParentCommandLine|contains|all:
            - ':\Users\'
            - '\AppData\Local\Microsoft\EdgeUpdate\Install\{'
            - '\EDGEMITMP_'
            - '.tmp\setup.exe'
            - '--install-archive='
            - '--previous-version='
            - '--msedgewebview --verbose-logging --do-not-launch-msedge --user-level'
    condition: selection and not 1 of filter_main_* and not 1 of filter_optional_*
falsepositives:
    - Unknown
level: medium