I just wanted to exclude .exe, .com., .bat., zip but allow most of extensions. With .xsl becoming .xslm, .xslx it is a bit of a maintenance to keep adding to the AllowedFileExtensions.
In general there is no build in functionality for setting not allowed files extensions. You could however try to manually filter the files and cancel the upload if a file with specific extension is being uploaded. In order to achieve this you should subscribe on the client-side OnClientFileUploading event and use the following implementation of the event handler function:
The above suggested solution will not upload files with zip extension.
Best wishes,
Dimitar Terziev
the Telerik team
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