The Contact module does not correctly handle certain user input when displaying category information. Users privileged to create contact categories can insert arbitrary HTML and script code into the contact module administration page. Such a cross-site scripting attack may lead to the malicious user gaining administrative access. Wikipedia has more information about cross-site scripting (XSS).
This issue affects Drupal 6.x and Drupal 5.x.
Vendor Status:
Drupal issued an update for this vulnerability