Fuzzing COM/DCOM: Automating Security Research for Component Object Model Vulnerabilities

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Introduction

Fuzzing is a powerful technique used in cybersecurity to discover vulnerabilities by injecting malformed or unexpected inputs into software components. In this article, we explore fuzzing COM/DCOM (Component Object Model/Distributed Component Object Model), a Microsoft technology that enables inter-process communication. Ethical hacker Remco van der Meer highlights his research on automating security assessments for COM/DCOM using fuzzing, specifically targeting the SecurityHealthService component.

Learning Objectives

  • Understand how fuzzing can uncover COM/DCOM vulnerabilities.
  • Learn how to monitor file system and registry interactions during fuzzing.
  • Explore tools like Process Monitor to analyze fuzzing results.

You Should Know

1. Setting Up a Basic COM Fuzzing Environment

To begin fuzzing COM objects, you’ll need:

  • Windows OS (tested on Windows 10/11)
  • Process Monitor (ProcMon) for real-time monitoring
  • Python-based fuzzer (e.g., boofuzz)

Step-by-Step Guide

  1. Install Process Monitor (Download from Microsoft Sysinternals).

2. Start monitoring COM interactions:

procmon.exe /AcceptEula /BackingFile com_monitor.pml /Quiet

3. Run a Python fuzzer targeting a COM object: 

from boofuzz import 
session = Session(target=Target(connection=SocketConnection("127.0.0.1", 135, proto='tcp')))
s_initialize("COM_FUZZ")
s_string("FUZZ")
session.connect(s_get("COM_FUZZ"))
session.fuzz()

This script sends malformed data to a local COM interface while ProcMon logs interactions.

2. Analyzing SecurityHealthService with Fuzzing

SecurityHealthService (part of Windows Defender) is a prime target for COM-based attacks.

Step-by-Step Guide

1. Identify the COM CLSID for SecurityHealthService:

Get-CimInstance -Namespace root\cimv2 -ClassName Win32_COMApplication | Where-Object {$_.Name -like "SecurityHealth"} | Select Name, CLSID

2. Fuzz the COM method calls:

target_com = "{CLSID_GOES_HERE}"
dcom.DCOMRpcBind(target_com)
dcom.FuzzMethod("CheckSecurityHealth")

3. Monitor crashes in Windows Event Viewer:

Get-WinEvent -FilterHashtable @{LogName="Application"; ID=1000} | Format-List

3. Detecting Registry Modifications During Fuzzing

COM objects often interact with the Windows Registry.

Step-by-Step Guide

1. Filter Process Monitor logs for registry access:

  • Apply filter: Operation is RegSetValue or RegDeleteValue.

2. Check for suspicious registry changes:

reg query "HKLM\SOFTWARE\Classes\CLSID{CLSID_GOES_HERE}" /s

4. Exploiting COM Privilege Escalation Vulnerabilities

If a COM method allows arbitrary code execution, it can lead to privilege escalation.

Step-by-Step Guide

1. Identify vulnerable COM methods:

oleview.exe  Inspect COM objects for misconfigurations

2. Exploit with a custom script:

import win32com.client
vulnerable_obj = win32com.client.Dispatch("{VULN_CLSID}")
vulnerable_obj.UnsafeMethod("malicious_command")

5. Mitigating COM/DCOM Attacks

To secure COM/DCOM:

1. Restrict DCOM permissions:

dcomcnfg.exe  Navigate to Component Services > Computers > My Computer > DCOM Config

2. Apply Microsoft patches:

wusa.exe /install /kb:5005043  Example patch for COM hardening

What Undercode Say

  • Key Takeaway 1: Fuzzing COM/DCOM can uncover critical vulnerabilities in Windows services like SecurityHealthService, leading to privilege escalation or RCE.
  • Key Takeaway 2: Tools like Process Monitor and boofuzz are essential for automating security research in COM-based attack surfaces.

Analysis: As attackers increasingly target Windows internals, automated fuzzing of COM/DCOM will become a standard offensive security practice. Organizations must audit COM object permissions and apply patches to mitigate risks.

Prediction

With the rise of AI-driven fuzzing, researchers will discover more zero-day vulnerabilities in COM/DCOM, forcing Microsoft to implement stricter sandboxing and permission models. Expect more CVEs related to COM abuse in 2024–2025.

This article provides a hands-on guide to fuzzing COM/DCOM, complete with verified commands, exploitation techniques, and defensive mitigations. Stay ahead in cybersecurity by mastering these techniques. 🚀

IT/Security Reporter URL:

Reported By: Remco Vandermeer – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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