Files With System DLL Name In Unsuspected Locations

title: Files With System DLL Name In Unsuspected Locations
id: 13c02350-4177-4e45-ac17-cf7ca628ff5e
status: test
description: |
    Detects the creation of a file with the ".dll" extension that has the name of a System DLL in uncommon or unsuspected locations. (Outisde of "System32", "SysWOW64", etc.).
    It is highly recommended to perform an initial baseline before using this rule in production.
references:
    - Internal Research
author: Nasreddine Bencherchali (Nextron Systems)
date: 2024-06-24
tags:
    - attack.defense-evasion
    - attack.t1036.005
logsource:
    category: file_event
    product: windows
detection:
    selection:
        TargetFilename|endswith:
            # Note: Add more System DLL that can be abused for DLL sideloading to increase coverage
            - '\secur32.dll'
            - '\tdh.dll'
    filter_main_generic:
        # Note: It is recommended to use a more robust filter instead of this generic one, to avoid false negatives.
        TargetFilename|contains:
            # - '\SystemRoot\System32\'
            - 'C:\$WINDOWS.~BT\'
            - 'C:\$WinREAgent\'
            - 'C:\Windows\SoftwareDistribution\'
            - 'C:\Windows\System32\'
            - 'C:\Windows\SysWOW64\'
            - 'C:\Windows\WinSxS\'
            - 'C:\Windows\uus\'
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Third party software might bundle specific versions of system DLLs.
# Note: Upgrade to high after an initial baseline to your environement.
level: medium
regression_tests_path: regression_data/rules/windows/file/file_event/file_event_win_creation_system_dll_files/info.yml