Windows Suspicious Defender Engine or Signature Files Created

name: Windows Suspicious Defender Engine or Signature Files Created
id: 42e848eb-1d5f-4ffb-88c2-088c4a6fdfb3
version: 1
creation_date: '2026-04-27'
modification_date: '2026-04-27'
author: Raven Tait, Splunk
status: production
type: Anomaly
description: |-
    Detects Windows Defender engine (mpengine.dll) or signature database files (*.vdm) being created by any process that is not a Windows Defender component.
    BlueHammer extracts these files from the downloaded mpam-fe update package into a UUID-named subdirectory of %TEMP% as part of staging the TOCTOU privilege escalation.
data_source:
    - Sysmon EventID 11
search: |-
    `sysmon` EventID="11"
    TargetFilename IN (
        "*\\mpasbase.vdm*",
        "*\\mpasdlta.vdm*",
        "*\\mpavbase.vdm*",
        "*\\mpavdlta.vdm*",
        "*\\mpengine.dll*"
    )
    NOT Image IN (
        "*:\\ProgramData\\Microsoft\\Windows Defender\\*",
        "*:\\Program Files\\Windows Defender\\*"
    )
    | fillnull
    | rename Computer as dest
    | stats count by dest TargetFilename Image EventID
                     action file_name file_path process_guid
                     process_id user vendor_product
    
    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    | `windows_suspicious_defender_engine_or_signature_files_created_filter`
how_to_implement: |-
    The detection is based on data that originates from Endpoint Detection and Response (EDR) agents. These agents are designed to provide security-related telemetry from the endpoints where the agent is installed. To implement this search, you must ingest logs that contain the process GUID, process name, and parent process. Additionally, you must ingest complete command-line executions. These logs must be processed using the appropriate Splunk Technology Add-ons that are specific to the EDR product. The logs must also be mapped to the `Processes` node of the `Endpoint` data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process.
known_false_positives: |-
    Some legitimate software updates or security tools may create Windows Defender engine or signature files in user temp folders during scanning or updating processes.
    Filter detections for trusted update utilities and system maintenance tasks.
references:
    - https://github.com/Nightmare-Eclipse/BlueHammer
intermediate_findings:
    entities:
        - field: dest
          type: system
          score: 20
          message: Windows Defender Engine or Signature file $file_path$ created by Non-Defender Process $Image$ on $dest$.
threat_objects:
    - field: Image
      type: process
analytic_story:
    - Windows Privilege Escalation
    - BlueHammer
asset_type: Endpoint
mitre_attack_id:
    - T1068
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: endpoint
security_domain: endpoint
cve:
    - CVE-2026-33825