Merge pull request from GHSA-9928-3cp5-93fm

* Fix attachments getting processed despite failing content-type validation

* Add a restrictive ImageMagick security policy tailored for Mastodon

* Fix misdetection of MP3 files with large cover art

* Reject unprocessable audio/video files instead of keeping them unchanged

lib/paperclip/media_type_spoof_detector_extensions.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+module Paperclip
+  module MediaTypeSpoofDetectorExtensions
+    def calculated_content_type
+      return @calculated_content_type if defined?(@calculated_content_type)
+
+      @calculated_content_type = type_from_file_command.chomp
+
+      # The `file` command fails to recognize some MP3 files as such
+      @calculated_content_type = type_from_marcel if @calculated_content_type == 'application/octet-stream' && type_from_marcel == 'audio/mpeg'
+      @calculated_content_type
+    end
+
+    def type_from_marcel
+      @type_from_marcel ||= Marcel::MimeType.for Pathname.new(@file.path),
+                                                 name: @file.path
+    end
+  end
+end
+
+Paperclip::MediaTypeSpoofDetector.prepend(Paperclip::MediaTypeSpoofDetectorExtensions)

lib/paperclip/transcoder.rb

@@ -19,10 +19,7 @@ module Paperclip
     def make
       metadata = VideoMetadataExtractor.new(@file.path)
 
-      unless metadata.valid?
-        Paperclip.log("Unsupported file #{@file.path}")
-        return File.open(@file.path)
-      end
+      raise Paperclip::Error, "Error while transcoding #{@file.path}: unsupported file" unless metadata.valid?
 
       update_attachment_type(metadata)
       update_options_from_metadata(metadata)