SA-2007-026 - Drupal Core - Cross site scripting via uploads

By Heine on 17 Oct 2007 at 18:38 UTC

Advisory ID: DRUPAL-SA-2007-026
Project: Drupal core
Version: 4.7.x, 5.x
Date: 2007-October-17
Security risk: Moderately critical
Exploitable from: Remote
Vulnerability: Cross site scripting

Description

The allowed extension list of the core Upload module contains the extension HTML by default. Such files can be used to execute arbitrary script code in the context of the affected site when a user views the file.

Revoking upload permissions or removing the .html extension from the allowed extension list will stop uploads of malicious files. but will do nothing to protect your site against files that are already present. Carefully inspect the file system path for any HTML files. We recommend you remove any HTML file you did not update yourself. You should look for

, CSS includes, Javascript includes, and onerror="" attributes if you need to review files individually.

Wikipedia has more information about cross site scripting (XSS).

Important note: Configuration change needed

Installing the upgrade or using the patch will not remove the .html extensions from an already configured upload module. Visit Administer » Site Configuration » File uploads (admin/settings/uploads) on Drupal 5.x or administer » settings » upload (admin/settings/upload) on Drupal 4.7.x to remove html from the allowed extensions lists.

The steps above will stop uploads of malicious files, but will do nothing to protect your site against files that have already been uploaded. Make sure to carefully inspect the file system path for any HTML files.