Uncommon File Created In Office Startup Folder

title: Uncommon File Created In Office Startup Folder
id: a10a2c40-2c4d-49f8-b557-1a946bc55d9d
status: test
description: Detects the creation of a file with an uncommon extension in an Office application startup folder
references:
    - https://app.any.run/tasks/d6fe6624-6ef8-485d-aa75-3d1bdda2a08c/
    - http://addbalance.com/word/startup.htm
    - https://answers.microsoft.com/en-us/msoffice/forum/all/document-in-word-startup-folder-doesnt-open-when/44ab0932-2917-4150-8cdc-2f2cf39e86f3
    - https://en.wikipedia.org/wiki/List_of_Microsoft_Office_filename_extensions
author: frack113, Nasreddine Bencherchali (Nextron Systems)
date: 2022-06-05
modified: 2023-12-13
tags:
    - attack.resource-development
    - attack.t1587.001
logsource:
    product: windows
    category: file_event
detection:
    selection_word_paths:
        - TargetFilename|contains: '\Microsoft\Word\STARTUP'
        - TargetFilename|contains|all:
              - '\Office'
              - '\Program Files'
              - '\STARTUP'
    filter_exclude_word_ext:
        TargetFilename|endswith:
            - '.docb' # Word binary document introduced in Microsoft Office 2007
            - '.docm' # Word macro-enabled document; same as docx, but may contain macros and scripts
            - '.docx' # Word document
            - '.dotm' # Word macro-enabled template; same as dotx, but may contain macros and scripts
            - '.mdb' # MS Access DB
            - '.mdw' # MS Access DB
            - '.pdf' # PDF documents
            - '.wll' # Word add-in
            - '.wwl' # Word add-in
    selection_excel_paths:
        - TargetFilename|contains: '\Microsoft\Excel\XLSTART'
        - TargetFilename|contains|all:
              - '\Office'
              - '\Program Files'
              - '\XLSTART'
    filter_exclude_excel_ext:
        TargetFilename|endswith:
            - '.xll'
            - '.xls'
            - '.xlsm'
            - '.xlsx'
            - '.xlt'
            - '.xltm'
            - '.xlw'
    filter_main_office_click_to_run:
        Image|contains: ':\Program Files\Common Files\Microsoft Shared\ClickToRun\'
        Image|endswith: '\OfficeClickToRun.exe'
    filter_main_office_apps:
        Image|contains:
            - ':\Program Files\Microsoft Office\'
            - ':\Program Files (x86)\Microsoft Office\'
        Image|endswith:
            - '\winword.exe'
            - '\excel.exe'
    condition: ((selection_word_paths and not filter_exclude_word_ext) or (selection_excel_paths and not filter_exclude_excel_ext)) and not 1 of filter_main_*
falsepositives:
    - False positive might stem from rare extensions used by other Office utilities.
level: high