Index: src/wp-includes/media.php
===================================================================
--- src/wp-includes/media.php	(revision 27139)
+++ src/wp-includes/media.php	(working copy)
@@ -826,7 +826,12 @@
 		'link'       => ''
 	), $attr, 'gallery'));
 
-	$id = intval($id);
+	$id = intval( $id );
+
+	if ( $id && ! current_user_can( 'read_post', $id ) ) {
+		return '';
+	}
+
 	if ( 'RAND' == $order )
 		$orderby = 'none';