Windows AppX Deployment Unsigned Package Installation

Detects attempts to install unsigned MSIX/AppX packages using the -AllowUnsigned parameter via AppXDeployment-Server events

title: Windows AppX Deployment Unsigned Package Installation
id: 9a025188-6f2d-42f8-bb2f-d3a83d24a5af
related:
    - id: 37651c2a-42cd-4a69-ae0d-22a4349aa04a
      type: similar
    - id: 975b2262-9a49-439d-92a6-0709cccdf0b2
      type: similar
status: experimental
description: Detects attempts to install unsigned MSIX/AppX packages using the -AllowUnsigned parameter via AppXDeployment-Server events
references:
    - https://docs.microsoft.com/en-us/powershell/module/appx/add-appxpackage
    - https://www.splunk.com/en_us/blog/security/msix-weaponization-threat-detection-splunk.html
author: Michael Haag, Swachchhanda Shrawan Poudel (Nextron Systems)
date: 2025-11-03
tags:
    - attack.execution
    - attack.defense-impairment
    - attack.t1204.002
    - attack.t1553.005
logsource:
    product: windows
    service: appxdeployment-server
detection:
    selection:
        EventID: 603
        Flags: '8388608'
    condition: selection
falsepositives:
    - Legitimate installation of unsigned packages for legitimate purposes such as development or testing
level: medium

• T1204.002Malicious File
• T1553.005Mark-of-the-Web Bypass

• https://docs.microsoft.com/en-us/powershell/module/appx/add-appxpackage↗
• https://www.splunk.com/en_us/blog/security/msix-weaponization-threat-detection-splunk.html↗