Blazor debugging fails in Visual Studio 18.11.2 but works in 18.11.1

         After upgrading from Visual Studio 18.11.1 to Visual Studio 18.11.2, Blazor debugging no longer works reliably.

Debugging starts, Microsoft Edge opens, but remains on about:blank and Visual Studio reports a debug adapter failure.

Downgrading to Visual Studio 18.11.1 immediately resolves the issue.

Environment

Visual Studio 2026 Professional 18.11.2

.NET 10.0.14

Blazor WebAssembly

Microsoft Edge

Windows 11

Issue Description

After upgrading Visual Studio from 18.11.1 to 18.11.2, launching a Blazor WebAssembly project with F5 fails.

Visual Studio displays:

One or more errors occurred.

Failed to launch debug adapter.

Additional information may be available in the output window.

Unable to launch browser:

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

Socket closed before the connection was established

Microsoft Edge opens but remains on: about:blank

Investigation Performed

Project Cleanup

Deleted: .vs, bin, obj

Rebuilt solution.

Result: Issue persists.

Visual Studio Reset

Executed: devenv /resetsettings

Result: Issue persists.

Safe Mode

Executed: devenv /safemode

Result: Issue persists.

Visual Studio Repair

Performed full Visual Studio repair using Visual Studio Installer.

Result: Issue persists.

ActivityLog Errors Observed

At one point the ActivityLog contained:

Microsoft.WebTools.BrowserLink.Package

SetSite failed for package [EurekaPackage]

System.NullReferenceException

Microsoft.WebTools.Languages.Html.VS

CssPackage

System.NullReferenceException

After repair these errors were no longer reproduced.

Port Investigation

While debugging, an exception was triggered:

System.IO.IOException

Failed to bind to address

http://127.0.0.1:5277

Address already in use.

Investigation showed: netstat -ano | findstr :5277

returned:  127.0.0.1:5277 LISTENING

PID 28120

which was: dotnet.exe

After terminating the process: taskkill /PID 28120 /F

the port became available.

Application Startup Verification

Visual Studio Output window reports:

Now listening on: https://localhost:7268

Now listening on: http://localhost:5277

Application started.

Hosting environment: Development

Application starts successfully and Kestrel binds correctly.

However: Microsoft Edge still opens to about:blank.

and debugging does not function correctly.

Expected Behavior

Visual Studio launches Edge.

Edge navigates to the application URL.

Blazor application loads.

Debugger attaches successfully.

Actual Behavior

Edge opens.

Edge remains on about:blank.

Debugger fails to attach correctly.

Application may start successfully in the background.

Visual Studio reports debug adapter or browser launch issues.

Additional Notes

Ctrl+F5 works.

dotnet run works.

Application starts normally.

Issue appears related to browser launch/debug adapter integration.

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

 

The issue is fully reproducible in Visual Studio 18.11.2 and disappears immediately after reverting to Visual Studio 18.11.1. This appears to be a regression introduced in 18.11.2 affecting Blazor WebAssembly debugging and browser launch integration.