--- libraries/common.inc.php.orig	2017-03-31 19:29:29.272464800 +0200
+++ libraries/common.inc.php	2017-03-31 19:30:35.553865459 +0200
@@ -858,7 +858,7 @@
                 . ' ' . $cfg['Server']['auth_type']
             );
         }
-        if (isset($_REQUEST['pma_password'])) {
+        if (isset($_REQUEST['pma_password']) && strlen($_REQUEST['pma_password']) > 256) {
             $_REQUEST['pma_password'] = substr($_REQUEST['pma_password'], 0, 256);
         }
         include_once  './libraries/plugins/auth/' . $auth_class . '.class.php';