This vulnerability is fixed in Drupal 4.5.6, 4.6.4 and onwards. Drupal's new XSS filter mechanism takes care of all vulnerabilities listed on http://ha.ckers.org/xss.html (and even more).
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Writing secure code
If you are a Drupal developer, please read the handbook section on Writing secure code.
Drupal Steward
Drupal Steward is a web application firewall product that can protect your Drupal sites from highly critical and mass exploitable vulnerabilities, allowing you to update on your own time.