Advanced Forum 6.x before 6.x-1.1, a module for Drupal, does not prevent users from modifying user signatures after the associated comment …

Advanced Forum 6.x before 6.x-1.1, a module for Drupal, does not prevent users from modifying user signatures after the associated comment format has been changed to an administrator-controlled input format, which allows remote authenticated users to inject arbitrary web script, HTML, and possibly PHP code via a crafted user signature.