Prevent from relaying arbitrary requests through modcss.inc (security issue)

program/steps/mail/func.inc

@@ -1194,15 +1194,16 @@ function rcmail_html4inline($body, $container_id, $body_id='', &$attributes=null
  */
 function rcmail_alter_html_link($matches)
 {
-  global $EMAIL_ADDRESS_PATTERN;
+  global $RCMAIL, $EMAIL_ADDRESS_PATTERN;
 
   $tag = $matches[1];
   $attrib = parse_attrib_string($matches[2]);
   $end = '>';
 
   if ($tag == 'link' && preg_match('/^https?:\/\//i', $attrib['href'])) {
-    $attrib['href'] = "?_task=utils&_action=modcss&u=" . urlencode($attrib['href'])
-        . "&c=" . urlencode($GLOBALS['rcmail_html_container_id']);
+    $tempurl = 'tmp-' . md5($attrib['href']) . '.css';
+    $_SESSION['modcssurls'][$tempurl] = $attrib['href'];
+    $attrib['href'] = $RCMAIL->url(array('task' => 'utils', 'action' => 'modcss', 'u' => $tempurl, 'c' => $GLOBALS['rcmail_html_container_id']));
     $end = ' />';
   }
   else if (preg_match('/^mailto:'.$EMAIL_ADDRESS_PATTERN.'(\?[^"\'>]+)?/i', $attrib['href'], $mailto)) {

program/steps/utils/modcss.inc

@@ -5,7 +5,7 @@
  | program/steps/utils/modcss.inc                                        |
  |                                                                       |
  | This file is part of the Roundcube Webmail client                     |
- | Copyright (C) 2007-2010, The Roundcube Dev Team                       |
+ | Copyright (C) 2007-2011, The Roundcube Dev Team                       |
  | Licensed under the GNU GPL                                            |
  |                                                                       |
  | PURPOSE:                                                              |
@@ -21,14 +21,14 @@
 
 $source = '';
 
-$url = preg_replace('![^a-z0-9:./\-_?$&=%]!i', '', $_GET['u']);
-if ($url === null) {
+$url = preg_replace('![^a-z0-9.-]!i', '', $_GET['_u']);
+if ($url === null || !($realurl = $_SESSION['modcssurls'][$url])) {
     header('HTTP/1.1 403 Forbidden');
-    echo $error;
+    echo "Unauthorized request";
     exit;
 }
 
-$a_uri = parse_url($url);
+$a_uri = parse_url($realurl);
 $port  = $a_uri['port'] ? $a_uri['port'] : 80;
 $host  = $a_uri['host'];
 $path  = $a_uri['path'] . ($a_uri['query'] ? '?'.$a_uri['query'] : '');
@@ -85,7 +85,7 @@ fclose($fp);
 $mimetype = strtolower($headers['content-type']);
 if (!empty($source) && in_array($mimetype, array('text/css','text/plain'))) {
     header('Content-Type: text/css');
-    echo rcmail_mod_css_styles($source, preg_replace('/[^a-z0-9]/i', '', $_GET['c']));
+    echo rcmail_mod_css_styles($source, preg_replace('/[^a-z0-9]/i', '', $_GET['_c']));
     exit;
 }
 else