How to restrict exe file upload in ASP.NET file upload control

You can't prevent the upload control from uploading a file based on it's content - as far as it's concerned, all files are just binary data, it doesn't care about the actual content. And ... text files are Unicode these days which use a wide spectrum of binary values, so it can be difficult to check if a file is "genuine text" or "binary data".

What you would have to do is check the file content at the backend: all EXE files start with the characters "MZ" and will generally contain a lot of null values so you could start by looking for that signature ...

But it probably won't help you: I don't know why you want to exclude EXE files specifically, but don;t forget it's pretty easy to ZIP them, translate them to Base64, encrypt them, or a combination of these methods. You probably need to think carefully about why you are trying to do this, and come up with a planned set of "permitted data" rather than trying to "ban" one class of file.