When accessing a malformed URL an HTTP error occurs and the user is shown the YSOD error page as shown on the following page.
Displaying a Custom Error Page (C#) | Microsoft Docs
Please implement a setting that will allow users to change the default error page that is displayed in these circumstances.
Comments
Custom error pages enable you to customize the pages that display when an error occurs. This makes your website appear more professional and also prevents visitors from leaving your site. If a visitor sees a generic error page, they are likely to leave your site.
Category: General