How can I prevent uploading bmp image?

Question

I need to prevent uploading bmp image for user. How can it be possible?

Answer 1

I have found the solution from here. And its working!

WordPress has a set of restricted filetypes it will allow you to upload via the media library. Whilst this is a great security feature, there may be times where you’d like to add other files that are restricted by default, or maybe even the opposite where you’d only like to allow a few extensions to be uploaded. Fortunately, WordPress makes this dead easy with a small snippet of PHP code.

If you’d like to add or remove a specific filetype that can be uploaded to wordpress via the media library, you can insert this PHP code in your theme functions.php file:

function my_myme_types($mime_types){
//Adjust the $mime_types, which is an associative array
//where the key is extension and value is mime type.
    return $mime_types;
}
add_filter('upload_mimes', 'my_myme_types', 1, 1);

Here is an example of what you can do to add and remove a new filetype (in this example, I’m adding an extension that already exists, but the concept is the same):

function my_myme_types($mime_types){
    $mime_types['avi'] = 'video/avi'; //Adding avi extension
    unset($mime_types['pdf']); //Removing the pdf extension
    return $mime_types;
}
add_filter('upload_mimes', 'my_myme_types', 1, 1);

You can also reset the allowed filetypes by creating a new array within the function and returning these values:

function my_myme_types($mime_types){
    //Creating a new array will reset the allowed filetypes
    $mime_types = array(
        'jpg|jpeg|jpe' => 'image/jpeg',
        'gif' => 'image/gif',
        'png' => 'image/png',
        'bmp' => 'image/bmp',
        'tif|tiff' => 'image/tiff'
    );
    return $mime_types;
}
add_filter('upload_mimes', 'my_myme_types', 1, 1);

If you’d like to see what filetypes are currently supported by wordpress, check out the function get_allowed_mime_types located in the wp-includes/functions.php file.

Answer 2

The magic is in get_allowed_mime_types() which calls the upload_mimes filter. That is filtering a default array consisting of keys as a non-terminated regular expression of file-extensions and the mapped mime-type as values:

array(
    'jpg|jpeg|jpe' => 'image/jpeg',
    'gif' => 'image/gif',
    'png' => 'image/png',
    'bmp' => 'image/bmp',
    'tif|tiff' => 'image/tiff',
    'ico' => 'image/x-icon',
    ....
}

so hooking into that filter and removing bmp should do the job for the moment:

/** prevent uploading of .bmp files. */
add_filter('upload_mimes', function(array $mimes)
    { 
        unset($mimes['bmp']);
        return $mimes;
    })
    ;

Just copy that over into a file named no-bmp-upload.php and place it into the wp-content\mu-plugins folder.