Open source software security

Drupal Embedded Media Field Module XSS Vulnerability

30 November -0001

Description of Vulnerability:

Drupal (http://drupal.org) is a robust content management system (CMS) written in PHP and MySQL. The Drupal Embedded Media Field module (http://drupal.org/project/emfield) "will create fields for content types that can be used to display video, image, and audio files from various third party providers" Unfortunately the Embedded Media Field module contains an arbitrary HTML injection vulnerability (also known as cross site scripting, or XSS) due to the fact that it fails to sanitize user supplied audio file paths and custom embed code.

Systems affected:

Drupal 6.19 with Embedded Media Field 6.x-1.25 and CCK 6.x-2.8 was tested and shown to be vulnerable

Impact

Users could inject arbitrary scripts into pages affecting other site users. This could result in administrative account compromise leading to web server process compromise. A more likely scenario would be for an attacker to inject hidden content (such as iframes, applets, or embedded objects) that would attack client browsers in an attempt to compromise site users' machines. This vulnerability could also be used to launch cross site request forgery (XSRF) attacks against the site that could have other unexpected consequences.

Mitigating factors:

In order to exploit this vulnerability the attacker must have the ability to edit content of a content type with an embedded media field.

Proof of concept:

  1. Install Drupal 6-19, CCK module, and Embedded Media Field module version 6.x-1.25
  2. Enable the Content, Embedded Media Field, Embedded Audio Field modules from ?q=/admin/build/modules
  3. Alter the default 'Story' content type at ?q=admin/content/node-type/story/fields
  4. Add a 'New Field' in the form at the bottom of this page with the label 'audio' the field name 'field_audio' the type 'Embedded Audio' and the form element '3rd Party Aduio' then click the 'Save' button
  5. Configure the new video field from ?q=admin/content/node-type/story/fields/field_video
  6. Select all content providers for convenience and click 'Save field settings' button at the bottom of the form
  7. Create a new piece of story content from ?q=node/add/story entering arbitrary values.
  8. Enter "'/><script>alert('xss');</script><embed onshow='alert("foo");' src='http://traffic.libsyn.com/pauldotcom/PaulDotCom-SW-217pt2.mp3" in the 'audio:' text field
  9. Click the 'Save' and observe the rendered JavaScript alert whenever the node is displayed

Patch:

Applying the following patch mitigates this issue in version 6.x-1.25


--- emfield/contrib/emaudio/providers/custom_url.inc	2009-06-26 14:31:00.000000000 -0400
+++ emfield/contrib/emaudio/providers/custom_url.inc	2010-11-05 15:17:08.000000000 -0400
@@ -110,6 +110,7 @@ function emaudio_custom_url_rss($item, $
 }
 
 function theme_emaudio_custom_url_flash($url = NULL, $width = 0, $height = 0, $field = NULL, $data = array(), $node = NULL, $autoplay = FALSE) {
+  $url=str_replace("'", '', $url);  //this should be a URL validator instead
   // Display the audio using Flowplayer if it's available.
   if (module_exists('flowplayer')) {
     $config = array(