Blazor debugging fails in Visual Studio 18.11.2 with "Failed to launch debug adapter" and browser remains on about:blank

Environment

Visual Studio 2026 Professional 18.11.2

.NET 10

Microsoft Edge

Windows 11

Issue Description

After upgrading Visual Studio from 18.11.1 to 18.11.2, Blazor applications can no longer be debugged using F5.

When starting debugging, Microsoft Edge launches but remains on about:blank. Visual Studio then displays the following error:

Failed to launch debug adapter.

Unable to launch browser:

Could not connect to debug target at http://localhost:<port>

Socket closed before the connection was established

Steps to Reproduce

1. Install or update to Visual Studio 18.11.2.
2. Create a new Blazor project.
3. Press F5 to start debugging.
4. Microsoft Edge opens and remains on about:blank.
5. Visual Studio displays the debug adapter error.

Expected Behavior

The browser should navigate to the application URL and the debugger should attach successfully.

Actual Behavior

The browser remains on about:blank and Visual Studio fails to attach the debugger.

Investigation Performed

• Reproduced on a brand-new Blazor project.
• Reproduced on existing Blazor projects.
• Ctrl+F5 works correctly.
• "dotnet run" works correctly.
• The application starts and runs normally outside Visual Studio debugging.
• JavaScript debugging for ASP.NET (Chrome and Edge) was disabled.
• The issue occurs only when starting debugging with F5.
• The browser opens but does not navigate to the application URL.
• Visual Studio displays the error before the debugger can attach.
• The issue is reproducible even with a newly created Blazor project.

Error Message

Failed to launch debug adapter.

Unable to launch browser:

Could not connect to debug target at http://localhost:<port>

Socket closed before the connection was established

Workaround

Downgrading Visual Studio from 18.11.2 to 18.11.1 immediately resolves the issue.

After reverting to 18.11.1:

• F5 debugging works correctly.
• Browser navigates to the application URL.
• Debugger attaches successfully.
• Both new and existing Blazor projects work as expected.

Regression

This appears to be a regression introduced in Visual Studio 18.11.2. The issue is fully reproducible in Visual Studio 18.11.2 and disappears immediately after reverting to Visual Studio 18.11.1.