This module enables you to turn a Drupal install into the Central Authentication System (CAS). It makes your database the primary location for other systems to use for authentication in a SSO environment.
The module doesn't sufficiently sanitize user-supplied field values configured to be included as attributes in a CAS server response.
This vulnerability is mitigated by the fact that an attacker must be authenticated, have the ability to enter XML into a user entity field, and that field be configured as a CAS Attribute source leading to an XML Element Injection vulnerability.