Windows AppX/MSIX Full Trust Package Installation via AppXDeployment Server

title: Windows AppX/MSIX Full Trust Package Installation via AppXDeployment Server
id: 13be4088-4f11-46bc-999f-87d70a824381
status: experimental
description: This rule identifies AppX/MSIX package installations where the deployment reports Full Trust, indicating the package can run with elevated privileges rather than in normal AppX container restrictions. Attackers may use full-trust packaging to increase execution impact and bypass typical containment expectations. It relies on AppXDeployment-Server telemetry, matching EventID 400 with HasFullTrust=true, while excluding known Microsoft and local Program Files sources and expected caller processes.
references:
  - https://www.splunk.com/en_us/blog/security/msix-weaponization-threat-detection-splunk.html
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/builtin/appxdeployment_server/win_appxpackaging_server_full_trust_package_installation.yml
author: Michael Haag, Swachchhanda Shrawan Poudel (Nextron Systems), Huntrule Team
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: 400
    HasFullTrust: true
  filter_main_legitpath:
    PackageSourceUri|startswith:
      - file:///C:/Program%20Files/
      - file:///C:/Program%20Files%20(x86)/
  filter_main_microsoft:
    - PackageSourceUri|startswith: https://go.microsoft.com/fwlink/?linkid
    - PackageSourceUri|contains:
        - .cdn.microsoft.com
        - .cdn.office.net/
  filter_main_callerprocess:
    CallingProcess|startswith:
      - sysprep.exe
      - svchost.exe,AppReadiness
  filter_optional_x_update:
    PackageSourceUri|startswith: x-windowsupdate://
  filter_optional_microsoftclient:
    PackageFullName|startswith: MicrosoftWindows.Client.
  condition: selection and not 1 of filter_main_* and not 1 of filter_optional_*
falsepositives:
  - Some legitimate applications installation which have been missed from filtering can generate fps, thus baselining and tuning is recommended before deploying to production
level: medium
license: DRL-1.1
related:
  - id: e54279c7-4910-4e2c-902c-c56a25b549f6
    type: derived