Validate file uploaded by its content in ASP.net

What you're looking for is called "magic numbers". File types have a sequence of binary data at the start of them that lets you know what the file type contains regardless of its extension. What you're going to have to do is find the magic numbers for the types you're interested in (gif, jpg, png, maybe pdf if you allow those) and check the files you have uploaded start with those numbers. If they don't then delete\reject them.

http://www.garykessler.net/library/file_sigs.html[^]

Some code to check for images, but you can adapt for any magic numbers;

http://stackoverflow.com/questions/670546/determine-if-file-is-an-image[^]

http://stackoverflow.com/questions/772388/c-sharp-how-can-i-test-a-file-is-a-jpeg[^]

If you google for things like "c# check image magic number" you'll find other examples.

if (fileupload.HasFile)
 {
     if (extension == ".exe"  || extension == ".apk" )
     {
     }
     else
     {
         // alert select only .exe or .apk files
     }
}

Here is the another most useful info i found.. thanks all

http://www.dotnetexpertguide.com/2011/05/validate-uploaded-image-content-in.html[^]