Windows: Command-Line Use of ms-appinstaller Protocol Handler for File Downloads

Alerts on Windows command lines invoking ms-appinstaller with an http source, indicating potential remote file download behavior.

FreeUnreviewedSigmamediumv1

windows-command-line-use-of-ms-appinstaller-protocol-handler-for-file-downloads-180c7c5c

title: "Windows: Command-Line Use of ms-appinstaller Protocol Handler for File Downloads"
id: 281d0f90-ee96-46f6-ba90-938f0de5b9c7
related:
  - id: 7cff77e1-9663-46a3-8260-17f2e1aa9d0a
    type: derived
  - id: 180c7c5c-d64b-4a63-86e9-68910451bc8b
    type: derived
status: test
description: This rule flags Windows process command lines that invoke the ms-appinstaller protocol handler with a source parameter containing an http URL. Attackers can use AppInstaller.EXE via protocol invocation to fetch remote content and store it in an AppInstaller cache location. The detection relies on process creation telemetry and matches the presence of both ms-appinstaller://?source= and http in the command line.
references:
  - https://lolbas-project.github.io/lolbas/Binaries/AppInstaller/
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_creation/proc_creation_win_susp_ms_appinstaller_download.yml
author: Nasreddine Bencherchali (Nextron Systems), Swachchhanda Shrawan Poudel, Huntrule Team
date: 2023-11-09
tags:
  - attack.execution
  - attack.stealth
  - attack.t1218
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    CommandLine|contains|all:
      - ms-appinstaller://?source=
      - http
  condition: selection
falsepositives:
  - Unknown
level: medium
license: DRL-1.1

What it detects

This rule flags Windows process command lines that invoke the ms-appinstaller protocol handler with a source parameter containing an http URL. Attackers can use AppInstaller.EXE via protocol invocation to fetch remote content and store it in an AppInstaller cache location. The detection relies on process creation telemetry and matches the presence of both ms-appinstaller://?source= and http in the command line.

Known false positives

Unknown

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.