Windows Developer-Signed MSIX Package Installation

name: Windows Developer-Signed MSIX Package Installation
id: 2c0427aa-982c-4e97-bc33-bddeda4fd095
version: 5
creation_date: '2025-08-18'
modification_date: '2026-05-13'
author: Michael Haag, Splunk
status: production
type: Anomaly
description: This detection identifies the installation of developer-signed MSIX packages that lack Microsoft Store signatures. All malicious MSIX packages observed in recent threat campaigns (including those from FIN7, Zloader/Storm-0569, and FakeBat/Storm-1113) were developer-signed rather than Microsoft Store signed. Microsoft Store apps have specific publisher IDs containing '8wekyb3d8bbwe' or 'cw5n1h2txyewy', while developer-signed packages lack these identifiers. This detection focuses on EventID 855 from the Microsoft-Windows-AppXDeployment-Server/Operational logs, which indicates a completed package installation.
data_source:
    - Windows Event Log AppXDeployment-Server 855
search: |-
    `wineventlog_appxdeploymentserver` EventCode=855 NOT PackageMoniker IN ("*8wekyb3d8bbwe*","*cw5n1h2txyewy*")
      | stats count min(_time) as firstTime max(_time) as lastTime values(PackageMoniker) as PackageMoniker
        BY dvc EventCode user_id
      | rename dvc as dest
      | `security_content_ctime(firstTime)`
      | `security_content_ctime(lastTime)`
      | `windows_developer_signed_msix_package_installation_filter`
how_to_implement: To implement this detection, you need to be collecting Windows Event logs from the Microsoft-Windows-AppXDeploymentServer/Operational channel. In Splunk, this typically requires the Windows TA and configuration to collect from this specific channel. Ensure your Windows event collection is properly configured to capture EventCode 855 from the Microsoft-Windows-AppXDeploymentServer/Operational log.
known_false_positives: Legitimate developer-signed applications that are not from the Microsoft Store will trigger this detection. Organizations should maintain a baseline of expected developer-signed applications in their environment and tune the detection accordingly. Common legitimate developer-signed applications include in-house developed applications and some third-party applications that are not distributed through the Microsoft Store.
references:
    - https://redcanary.com/blog/threat-intelligence/msix-installers/
    - https://learn.microsoft.com/en-us/windows/win32/appxpkg/troubleshooting
    - https://www.advancedinstaller.com/msix-installation-or-launching-errors-and-fixes.html
    - https://redcanary.com/blog/threat-detection/code-signing-certificates/
intermediate_findings:
    entities:
        - field: dest
          type: system
          score: 20
          message: A developer-signed MSIX package "$PackageMoniker$" was installed on $dest$ by user $user_id$.
threat_objects:
    - field: PackageMoniker
      type: file_name
analytic_story:
    - MSIX Package Abuse
asset_type: Endpoint
mitre_attack_id:
    - T1553.005
    - T1204.002
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: endpoint
security_domain: endpoint