IIS Express fails to serve web apps in Visual Studio after Windows 11 24H2 update

[AlanForsTampa]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

IIS Express Fails to Serve Web Applications in Visual Studio After Windows 11 24H2 Update

Submitted by: Alan Fors
Location: Clearwater, FL
Role: Senior Software Engineer

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🖥️ Environment

• Windows 11 Version: Insider Preview 10.0.26200.5722 (ge_release_upr), installed July 30, 2025
• Visual Studio Versions: 2022 (latest), 2019
• IIS Express: Both 32-bit and 64-bit tested
• .NET Versions: .NET Framework 4.8, .NET 6, .NET 8

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🐞 Issue Summary

Starting Monday, August 4, 2025, all web applications fail to run in Visual Studio using IIS Express. This includes projects targeting .NET Framework and .NET Core/.NET 8. The issue is consistent across multiple Visual Studio versions and project types.

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❗ Symptoms

• HTTP: ERR_CONNECTION_RESET
• HTTPS: ERR_HTTP2_PROTOCOL_ERROR
• IIS Express process starts but shows low memory usage and no response
• No firewall or antivirus interference
• SSL certificates regenerated and trusted
• 32-bit IIS Express tested
• HTTP/2 disabled via registry
• Manual SSL binding attempted via IisExpressAdminCmd.exe
• Switching to Kestrel works, but IIS Express remains broken

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🔁 Steps to Reproduce

1. Open any web application in Visual Studio.
2. Set launch profile to IIS Express.
3. Run the application.
4. Observe browser errors and IIS Express behavior.

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✅ Expected Behavior

Web application should launch and respond via IIS Express as it did prior to August 4.

❌ Actual Behavior

Browser fails to connect. IIS Express appears to start but does not serve content.

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🛠️ Temporary Workaround

Switching to Kestrel works, but this is not viable for all workflows.

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🙏 Request

Please investigate compatibility issues between IIS Express and Windows 11 24H2. A fix or official workaround is needed for developers relying on IIS Express in Visual Studio.

Expected Behavior

No response

Steps To Reproduce

No response

Exceptions (if any)

No response

.NET Version

No response

Anything else?

No response

[halter73]

I'm not aware of any regressions with IIS Express. Do you see any logs in the Windows Event Viewer? This shows an app starting successfully.

Also, out of curiosity, why does Kestrel not suit your needs for local development?

[gomez34]

Same error here!

[AlanForsTampa]

I can (and do) use kestrel for my newer .net 6 & 8 projects, but I also maintain a framework 4.8 MVC app that is in production, and need IIS Express for that. I do not see that in event viewer but will look more closely today as I fight with it more. Alan Fors Vispero™ | Sr. Software Engineer 17757 US Hwy 19 North – Suite 200, Clearwater, FL 33764 T 727-803-8000 F 727-803-8001 ***@***.******@***.***> www.vispero.com<http://www.vispero.com/>

…

________________________________ From: Stephen Halter ***@***.***> Sent: Wednesday, August 6, 2025 7:01 PM To: dotnet/aspnetcore ***@***.***> Cc: Alan Fors ***@***.***>; Mention ***@***.***> Subject: Re: [dotnet/aspnetcore] IIS Express fails to serve web apps in Visual Studio after Windows 11 24H2 update (Issue #63160) You don't often get email from ***@***.*** Learn why this is important<https://aka.ms/LearnAboutSenderIdentification> CAUTION:EXTERNAL EMAIL SENDER! [https://avatars.githubusercontent.com/u/54385?s=20&v=4]halter73 left a comment (dotnet/aspnetcore#63160)<#63160 (comment)> I'm not aware of any regressions with IIS Express. Do you see any logs in the Windows Event Viewer? This shows an app starting successfully. image.png (view on web)<https://github.com/user-attachments/assets/d834d912-9dcb-4c83-bd6d-7a974055ec80> Also, out of curiosity, why does Kestrel not suit your needs for local development? — Reply to this email directly, view it on GitHub<#63160 (comment)>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/A66INMDS7ZLJ3LXXW6H4ERT3MKCMNAVCNFSM6AAAAACDI6HPLKVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTCNRRHA3DMMZZGI>. You are receiving this because you were mentioned.Message ID: ***@***.***>

[AlanForsTampa]

Just checked again and absolutely do NOT see the IIS Express startup event in event viewer. However, netstat does show a processes listening on the port until I stop the app in the debugger. Curiously, it's a system service listening, and it stops listening when I stop the app.

[AlanForsTampa]

PID 4 starts listening on the port configured for IIS express as soon as I start the app in the VS debugger. Task manager shows PID 4 as System, running as User SYSTEM. The executable running is ntoskrnl.exe and was last modified at 8/4/2025 11:19 AM, which is right when this problem started for me. It corresponds to a windows update done then:
Cumulative Update for Windows 11 Insider Preview (KB5062673) (26200.5733)
This must have been what caused the problem.

[AlanForsTampa]

Uninstalling the windows update for KB5062673 reverted ntoskrnl.exe to a version with a timestamp of 7/30/2025 (version 10.0.26100.5722) but that still did not resolve the problem. 😕

[AlanForsTampa]

After uninstalling update KB5062673 and rebooting, windows update decided to install two other updates:
2025-07 Cumulative Update for .NET Framework 3.5 and 4.8.1 for Windows 11, version 24H2 for x64 (KB5056579)
2025-08 .NET 8.0.19 Update for x64 Client (KB5064838)

After the required reboot for those, my IIS Express now works. I will close this now, but there was something seriously wrong.