Excel Desktop crashes when closing authentication dialog opened via displayDialogAsync (works on Web and Mac)

[valse]

Provide required information needed to triage your issue

Your Environment

• Platform [PC desktop, Mac, iOS, Office on the web]: PC desktop
• Host [Excel, Word, PowerPoint, etc.]: Excel
• Office version number: **Microsoft® Excel® for Microsoft 365 MSO (Version 2509 Build 16.0.19231.20246) 64-bit **
• Operating System: Windows 11
• Browser (if using Office on the web): Edge

Expected behavior

Closing an authentication dialog opened via Office.context.ui.displayDialogAsync should close cleanly and allow the add-in to continue functioning normally.

Current behavior

On Excel for Windows desktop, when the authentication dialog sends a message back to the host and the add-in calls dialog.close() inside the DialogMessageReceived callback, Excel crashes completely.

This issue does not occur in:

• Excel on the web
• Excel for Mac

If the dialog is not closed, Excel does not crash, but the authentication flow cannot properly complete.
The behavior started a few days ago and appears to be related to a possible update in the office.js CDN, because older and newer versions of our add-in now show the same issue despite no code changes on our side.

Steps to reproduce

1. Call Office.context.ui.displayDialogAsync to open an authentication dialog.
2. Perform authentication in the dialog and post a message back to the add-in.
3. In the dialog message callback (DialogMessageReceived), invoke dialog.close().
4. Excel for Windows desktop crashes immediately.

Provide additional details

1. The same authentication and dialog-handling code has been stable for a long time.
2. The crash began occurring without any updates to our add-in.
3. The crash is 100% reproducible on Windows desktop.
4. It happens when the local Wef folder cache is cleared

Context

This issue prevents users on Windows desktop from completing authentication (OAuth/Azure AD), effectively making the add-in unusable for them. We cannot release updates or provide a workaround until this regression is fixed.

Thank you for taking the time to review this issue. Our add-in is currently blocked on Windows desktop due to this regression.

[github-actions]

This issue was automatically labeled as a regression based on dual-LLM analysis of the issue content and comments.

Reason: The issue is identified as a regression because the functionality of closing an authentication dialog via Office.context.ui.displayDialogAsync previously worked without causing Excel to crash. The problem started occurring recently without any changes to the add-in's code, suggesting that a recent update, likely in the office.js CDN, introduced the bug. The issue is specific to Excel on Windows desktop and does not occur on other platforms like Excel on the web or Mac, further indicating a regression in the Windows-specific implementation. The fact that the crash is 100% reproducible and the same code was stable before strongly supports the conclusion that this is a regression.

[valse]

I did some additional investigation and I think I’ve narrowed down the root cause or at least the trigger condition.

In my authentication dialog I offer two possible login options:

1. Windows authentication (via a button)
2. Traditional username/password HTML form

What I found

• If I authenticate using Windows authentication, everything works correctly.
  The dialog closes at runtime and the add-in initializes normally.

• If I authenticate using the login form, Excel Desktop shows a password save prompt from the embedded browser (WebView).

This does not appear on Excel Online or Excel for Mac.

Unexpected behavior related to the password prompt

• If I do nothing with the save-password prompt and let the dialog close itself, the task pane reloads unexpectedly, and in some cases Excel crashes as described earlier.
• If I manually close the password prompt quickly before the dialog container closes, then the add-in continues and everything works as expected.

So the problematic behavior seems directly related to the embedded browser’s password manager prompt inside Excel Desktop.

I don’t remember ever seeing this prompt in the past, and I never had issues closing the dialog before.
That’s why I suspect something may have changed recently on the host side (WebView, Office.js runtime, or security policies).

The problem

I cannot rely on users:

• noticing the password-save popup
• dismissing it quickly enough
• or even understanding why it affects the add-in

This makes the login flow unreliable, since closing the dialog may trigger a crash or a full reload if the save-password dialog is still visible.

Question

Is there a way to disable the password-save prompt for dialogs opened with displayDialogAsync?

Since using a login form inside a dialog is a very common pattern for Office add-ins, I’m not sure if this issue affects only my scenario or if this could impact many add-ins relying on HTML authentication.

Any guidance on how to prevent the embedded WebView from showing the password manager prompt (or handle it safely) would be greatly appreciated.

Thanks!