Fix XSS vulnerability in _mbox argument handling (#1490417)

CHANGELOG

@@ -39,6 +39,7 @@ RELEASE 1.1.2
 - Fix potential info disclosure issue by protecting directory access (#1490378)
 - Fix blank image in html_signature when saving identity changes (#1490412)
 - Installer: Use openssl_random_pseudo_bytes() (if available) to generate des_key (#1490402)
+- Fix XSS vulnerability in _mbox argument handling (#1490417)
 
 RELEASE 1.1.1
 -------------

program/include/rcmail.php

@@ -1822,7 +1822,7 @@ class rcmail extends rcube
             }
             else {
                 $error = 'servererrormsg';
-                $args  = array('msg' => $err_str);
+                $args  = array('msg' => rcube::Q($err_str));
             }
         }
         else if ($err_code < 0) {