Restricting file uploads by type

Here is a hook to limit allowed uploads to images:

public function restrict_uploads() {
		if( is_admin() ) return;
		//if( current_user_can( 'unfiltered_upload' ) ) return;

		add_filter('wp_handle_upload_prefilter', function($file) {
			$allowed_mime_types = array('image/jpeg','image/gif','image/png'
				,'image/bmp','image/tiff');
			if( !in_array($file['type'], $allowed_mime_types) )
				$file['error'] = 'Only image files of the follow types are allowed for
					upload: .jpg, .jpeg, .jpe, .gif, .png, .bmp, .tif, .tiff';
			return $file;
		});
	}
add_action('bbp_edit_reply', 'restrict_uploads', 9);
        add_action('bbp_edit_topic', 'restrict_uploads', 9);
        add_action('bbp_new_reply', 'restrict_uploads', 9);
        add_action('bbp_new_topic', 'restrict_uploads', 9);

Add that to your functions.php.

There is a bug in the plugin you will have to fix as well in /code/attachments/front.php. Staring around line 118 change this:

if (!is_wp_error($upload)) {
                        	$errors->add('wp_upload', $upload->errors['wp_upload_error'][0], $file_name);
						} else {
                            $errors->add('wp_upload', $upload->errors['wp_upload_error'][0], $file_name);
                        }

to this:

if (is_wp_error($upload)) {
                        	$errors->add('wp_upload', $upload->errors['wp_upload_error'][0], $file_name);
                        } elseif (!empty($upload['error'])) {
                        	$errors->add('wp_upload', $upload['error'], $file_name);
						} else {
                            $uploads[] = $upload;
                        }

https://ww.wp.xz.cn/plugins/gd-bbpress-attachments/