Windows AppX Deployment Unsigned Package Installation — Sigma Rule

Rule metadata and linked tags

Author: Michael Haag, Swachchhanda Shrawan Poudel (Nextron Systems). Source status: experimental; severity: medium. Source dates: 2025-11-03 / not supplied.

{
  "product": "windows",
  "service": "appxdeployment-server"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 8cf6f67f9d1ccad7d9e20c86a318f67dbc054d00a29a76a7db4646d7014428c2

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: 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

Original YAML and metadata in JSON

False positives

• Legitimate installation of unsigned packages for legitimate purposes such as development or testing

Source 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