This page provides solutions for common problems you may encounter while working with the Telerik UI Upload HtmlHelper.
The issue is caused by a bug in Safari and occurs only when the Windows authentication and disabled Anonymous Authentication setting is enabled. It is reproducible with a standard
<input type="file" name="file" enctype="multipart/form-data" /> HTML element in ASP.NET Core and Web Forms applications.
Because the File Browser dialogs of the Telerik UI Editor for ASP.NET Core rely on the Upload control, the issue might occur when uploading images and other files through them on MAC Safari.
Solution The solution solely depends on a dedicated decision by Apple about whether and when to fix this browser issue. However, you can work around it by applying the suggestions provided in the Programmatically enable or disable anonymous authentication in IIS StackOverflow thread. This means to build a separate web service for file upload with an authentication setting, such as Anonymous for Safari scenarios, and the main application authentication setting, such as Windows Authentication.