IIS Application Pools Crash When OneAgent Deep Monitoring Is Enabled (ConfuserEx Obfuscation)

[bhaveshbjoshi]

• Summary
• Problem
• Troubleshooting steps
• Resolution
• What's next

*Use a table of contents for longer articles. 

Summary

This community article applies to Dynatrace OneAgent for Windows /.NET running on Microsoft IIS with deep monitoring enabled. It helps you diagnose and resolve IIS application pool crashes that occur because the application is obfuscated with ConfuserEx or a similar tool, which includes protection that terminates the process when a instrumentation is detected.

Problem

• IIS application pools crash shortly after application startup when OneAgent deep monitoring is enabled.

• Dynatrace OneAgent logs show that assemblies/modules cannot be instrumented
• Example logs line from OneAgent logs -

  Module is unsupported (obfuscated or unsupported version). Skipping instrumentation. (AppConfig.dll)
  

Why this happens

ConfuserEx is a .NET obfuscation tool that includes anti‑debugging and anti‑tampering protections.

When ConfuserEx detects:

• a debugger,
• a profiler,
• or runtime instrumentation (such as Dynatrace OneAgent deep monitoring), it intentionally terminates the process by calling:

  Environment.FailFast

This behavior is implemented directly in ConfuserEx, as shown here: 

ConfuserEx source (AntiDebug.Safe.cs)

https://github.com/yck1509/ConfuserEx/blob/v1.0.0/Confuser.Runtime/AntiDebug.Safe.cs#L13

 Microsoft documentation- Environment.FailFast Method

https://learn.microsoft.com/en-us/dotnet/api/system.environment.failfast

It's important to note that Applications using ConfuserEx are known to be incompatible with the Dynatrace OneAgent, and crashes in such scenarios are expected. As a result, using ConfuserEx with the Dynatrace .NET agent is not supported.

Troubleshooting steps

• Confirm with the application Developers whether ConfuserEx or any other obfuscator is used. 
• Check for OneAgent logs with entry - Module is unsupported (obfuscated or unsupported version). Skipping instrumentation. (AppConfig.dll)
• Check the windows event logs. You may search for following entry in the Windows Events.

Resolution

Option 1: Disable deep monitoring for the affected process group.
Option 2: Rebuild the application without ConfuserEx obfuscation.

What's next

If this article did not help, please open a support ticket, mention that this article was used and provide the following in the ticket:

• OneAgent Support Archive from the affected host.