COM Hijacking via TreatAs

Hunt Hypothesis

Detect modification of TreatAs key to enable “rundll32.exe -sta” command

Detection Rule

Sigma (Original)

title: COM Hijacking via TreatAs
id: dc5c24af-6995-49b2-86eb-a9ff62199e82
status: test
description: Detect modification of TreatAs key to enable "rundll32.exe -sta" command
references:
    - https://github.com/redcanaryco/atomic-red-team/blob/40b77d63808dd4f4eafb83949805636735a1fd15/atomics/T1546.015/T1546.015.md
    - https://www.youtube.com/watch?v=3gz1QmiMhss&t=1251s
author: frack113
date: 2022-08-28
modified: 2025-07-11
tags:
    - attack.privilege-escalation
    - attack.persistence
    - attack.t1546.015
logsource:
    category: registry_set
    product: windows
detection:
    selection:
        TargetObject|endswith: 'TreatAs\(Default)'
    filter_office:
        Image|startswith: 'C:\Program Files\Common Files\Microsoft Shared\ClickToRun\'
        Image|endswith: '\OfficeClickToRun.exe'
    filter_office2:
        Image:
            - 'C:\Program Files\Microsoft Office\root\integration\integrator.exe'
            - 'C:\Program Files (x86)\Microsoft Office\root\integration\integrator.exe'
    filter_svchost:
        # Example of target object by svchost
        # TargetObject: HKLM\SOFTWARE\Microsoft\MsixRegistryCompatibility\Package\Microsoft.Paint_11.2208.6.0_x64__8wekyb3d8bbwe\User\SOFTWARE\Classes\CLSID\{0003000A-0000-0000-C000-000000000046}\TreatAs\(Default)
        # TargetObject: HKU\S-1-5-21-1000000000-000000000-000000000-0000_Classes\CLSID\{0003000A-0000-0000-C000-000000000046}\TreatAs\(Default)
        Image: 'C:\Windows\system32\svchost.exe'
    filter_misexec:
        # This FP has been seen during installation/updates
        Image:
            - 'C:\Windows\system32\msiexec.exe'
            - 'C:\Windows\SysWOW64\msiexec.exe'
    condition: selection and not 1 of filter_*
falsepositives:
    - Legitimate use
level: medium

KQL (Azure Sentinel)

imRegistry
| where RegistryKey endswith "TreatAs\\(Default)" and (not(((ActingProcessName startswith "C:\\Program Files\\Common Files\\Microsoft Shared\\ClickToRun\\" and ActingProcessName endswith "\\OfficeClickToRun.exe") or (ActingProcessName in~ ("C:\\Program Files\\Microsoft Office\\root\\integration\\integrator.exe", "C:\\Program Files (x86)\\Microsoft Office\\root\\integration\\integrator.exe")) or ActingProcessName =~ "C:\\Windows\\system32\\svchost.exe" or (ActingProcessName in~ ("C:\\Windows\\system32\\msiexec.exe", "C:\\Windows\\SysWOW64\\msiexec.exe")))))

Required Data Sources

False Positive Guidance

• Legitimate use

MITRE ATT&CK Context

• Tactic: Privilege Escalation
• Tactic: Persistence
• Technique: T1546.015 — T1546.015

References

• https://github.com/redcanaryco/atomic-red-team/blob/40b77d63808dd4f4eafb83949805636735a1fd15/atomics/T1546.015/T1546.015.md
• https://www.youtube.com/watch?v=3gz1QmiMhss&t=1251s
• SigmaHQ Rule