Files With System DLL Name In Unsuspected Locations — Sigma Rule

Rule metadata and linked tags

Author: Nasreddine Bencherchali (Nextron Systems). Source status: test; severity: medium. Source dates: 2024-06-24 / not supplied.

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

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 7a6e900e83d5dea3c42aa1912f02d78d03c1349304240157140dc0bf76a386e5

Detection logic

Original source YAML. Source-tag agreement is not proof of complete semantic coverage. This rule has not been compiled for a SIEM backend or validated against live telemetry here.

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.stealth
    - 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

Original YAML and metadata in JSON

False positives

• Third party software might bundle specific versions of system DLLs.

Source references

• Internal Research (source note; no public URL supplied)