Drupal Embedded Media Field Cross Site Scripting

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Details of this disclosure can also be found at  
http://www.madirish.net/?article=474  
  
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  
filenames of thumbnail images before display.  
  
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.  
Also, many operating systems prevent the creation of files with slashes  
in their names so clever use of scripting without slashes is required to  
exploit this vulnerability.  
  
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 Media Thumbnail  
and Embedded Video 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 'video' the field name 'field_video' the type 'Embedded Video' and  
the form element '3rd Party Video' then click the 'Save' button  
5. Configure the new video field from  
?q=admin/content/node-type/story/fields/field_video  
6. Select YouTube as a content provider for convenience and be sure  
'Allow custom thumbnails for this field' is checked 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. For the 'Video custom thumbnail' choose an image with  
a name like "<image src='no.jpg' onerror='alert("xss")'>.png" and click  
the 'Upload' button  
8. Observe the rendered javascript alert dialogue  
9. Click the 'Save' button so that the XSS persists to future node edits  
  
Patch:  
- ------------------------------------------  
Applying the following patch mitigates this issue in version 6.x-1.25  
  
- --- emfield/contrib/emthumb/emthumb.module 2010-07-19 11:12:47.000000000  
- -0400  
+++ emfield/contrib/emthumb/emthumb.module 2010-11-04 16:10:48.000000000  
- -0400  
@@ -157,7 +157,7 @@ function emthumb_widget_element_process(  
  
$element['emthumb']['description'] = array(  
'#type' => 'markup',  
- - '#value' => '<strong>'. t('Filename:') .' </strong>'.  
$file['filename'],  
+ '#value' => '<strong>'. t('Filename:') .' </strong>'.  
check_plain($file['filename']),  
);  
  
// Overwrite with an input field if custom_alt is flagged.  
  
Vendor Response  
- ---------------  
http://drupal.org/node/992924  
  
  
- --   
Justin Klein Keane  
http://www.MadIrish.net  
  
The digital signature on this message can be confirmed using  
the public key at http://www.madirish.net/gpgkey  
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