Content filter for embedded attachments to protect from XSS on IE<=8 (#1487895)

CHANGELOG

@@ -1,6 +1,7 @@
 CHANGELOG Roundcube Webmail
 ===========================
 
+- Add content filter for embedded attachments to protect from XSS on IE (#1487895)
 - Use strpos() instead of strstr() when possible (#1488211)
 - Fix handling HTML entities when converting HTML to text (#1488212)
 - Fix fit_string_to_size() renders browser and ui unresponsive (#1488207)

program/include/rcube_message.php

@@ -142,10 +142,10 @@ class rcube_message
      * @param string $mime_id Part MIME-ID
      * @return string URL or false if part does not exist
      */
-    public function get_part_url($mime_id)
+    public function get_part_url($mime_id, $embed = false)
     {
         if ($this->mime_parts[$mime_id])
-            return $this->opt['get_url'] . '&_part=' . $mime_id;
+            return $this->opt['get_url'] . '&_part=' . $mime_id . ($embed ? '&_embed=1' : '');
         else
             return false;
     }
@@ -511,7 +511,7 @@ class rcube_message
                 $img_regexp = '/^image\/(gif|jpe?g|png|tiff|bmp|svg)/';
 
                 foreach ($this->inline_parts as $inline_object) {
-                    $part_url = $this->get_part_url($inline_object->mime_id);
+                    $part_url = $this->get_part_url($inline_object->mime_id, true);
                     if ($inline_object->content_id)
                         $a_replaces['cid:'.$inline_object->content_id] = $part_url;
                     if ($inline_object->content_location) {

program/steps/mail/func.inc

@@ -551,7 +551,7 @@ function rcmail_check_safe(&$message)
  * @param array  CID map replaces (inline images)
  * @return string Clean HTML
  */
-function rcmail_wash_html($html, $p = array(), $cid_replaces)
+function rcmail_wash_html($html, $p, $cid_replaces)
 {
   global $REMOTE_OBJECTS;
 
@@ -1068,7 +1068,7 @@ function rcmail_message_body($attrib)
       ) {
         $out .= html::tag('hr') . html::p(array('align' => "center"),
           html::img(array(
-            'src' => $MESSAGE->get_part_url($attach_prop->mime_id),
+            'src' => $MESSAGE->get_part_url($attach_prop->mime_id, true),
             'title' => $attach_prop->filename,
             'alt' => $attach_prop->filename,
           )));

program/steps/mail/get.inc

@@ -146,11 +146,24 @@ else if (strlen($pid = get_input_value('_part', RCUBE_INPUT_GET))) {
 
       header("Content-Disposition: $disposition; filename=\"$filename\"");
 
-      // turn off output buffering and print part content
-      if ($part->body)
-        echo $part->body;
-      else if ($part->size)
-        $IMAP->get_message_part($MESSAGE->uid, $part->mime_id, $part, true);
+      // do content filtering to avoid XSS through fake images
+      if (!empty($_REQUEST['_embed']) && $browser->ie && $browser->ver <= 8) {
+        if ($part->body)
+          echo preg_match('/<(script|iframe|object)/i', $part->body) ? '' : $part->body;
+        else if ($part->size) {
+          $stdout = fopen('php://output', 'w');
+          stream_filter_register('rcube_content', 'rcube_content_filter') or die('Failed to register content filter');
+          stream_filter_append($stdout, 'rcube_content');
+          $IMAP->get_message_part($MESSAGE->uid, $part->mime_id, $part, false, $stdout);
+        }
+      }
+      else {
+        // turn off output buffering and print part content
+        if ($part->body)
+          echo $part->body;
+        else if ($part->size)
+          $IMAP->get_message_part($MESSAGE->uid, $part->mime_id, $part, true);
+      }
     }
 
     exit;
@@ -178,3 +191,39 @@ header('HTTP/1.1 404 Not Found');
 exit;
 
 
+
+/**
+ * PHP stream filter to detect html/javascript code in attachments
+ */
+class rcube_content_filter extends php_user_filter
+{
+  private $buffer = '';
+  private $cutoff = 2048;
+
+  function onCreate()
+  {
+    $this->cutoff = rand(2048, 3027);
+    return true;
+  }
+
+  function filter($in, $out, &$consumed, $closing)
+  {
+    while ($bucket = stream_bucket_make_writeable($in)) {
+      $this->buffer .= $bucket->data;
+
+      // check for evil content and abort
+      if (preg_match('/<(script|iframe|object)/i', $this->buffer))
+        return PSFS_ERR_FATAL;
+
+      // keep buffer small enough
+      if (strlen($this->buffer) > 4096)
+        $this->buffer = substr($this->buffer, $this->cutoff);
+
+      $consumed += $bucket->datalen;
+      stream_bucket_append($out, $bucket);
+    }
+
+    return PSFS_PASS_ON;
+  }
+}
+

program/steps/mail/show.inc

@@ -132,7 +132,7 @@ function rcmail_message_attachments($attrib)
 
         $ol .= html::tag('li', null,
           html::a(array(
-            'href' => $MESSAGE->get_part_url($attach_prop->mime_id),
+            'href' => $MESSAGE->get_part_url($attach_prop->mime_id, false),
             'onclick' => sprintf(
               'return %s.command(\'load-attachment\',{part:\'%s\', mimetype:\'%s\'},this)',
               JS_OBJECT_NAME,