Detectionmediumtest

Rundll32 Execution With Uncommon DLL Extension

Detects the execution of rundll32 with a command line that doesn't contain a common extension

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Tim Shelton, Florian Roth (Nextron Systems), Yassine OukessouCreated Thu Jan 13Updated Thu Apr 04c3a99af4-35a9-4668-879e-c09aeb4f2bdfwindows

Log Source

WindowsProcess Creation

ProductWindows← raw: windows

CategoryProcess Creation← raw: process_creation

Events generated when a new process is spawned on the system. Covers command-line arguments, parent/child relationships, and process metadata.

Detection Logic

detection:
    selection:
        - Image|endswith: '\rundll32.exe'
        - OriginalFileName: 'RUNDLL32.EXE'
    filter_main_null:
        CommandLine: null
    filter_main_empty:
        CommandLine: ''
    filter_main_known_extension:
        - CommandLine|contains:
              # Note: This aims to cover: single and double quotes in addition to spaces and comma "," usage.
              - '.cpl '
              - '.cpl,'
              - '.cpl"'
              - ".cpl'"
              - '.dll '
              - '.dll,'
              - '.dll"'
              - ".dll'"
              - '.inf '
              - '.inf,'
              - '.inf"'
              - ".inf'"
        - CommandLine|endswith:
              # Note: This aims to cover: single and double quotes in addition to spaces and comma "," usage.
              - '.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_*