source: https://www.securityfocus.com/bid/24253/info
  
PHP JackKnife is prone to multiple input-validation vulnerabilities, including cross-site scripting and SQL-injection issues.
  
Exploiting these issues could allow an attacker to steal cookie-based authentication credentials, compromise the application, access or modify data, or exploit latent vulnerabilities in the underlying database implementation.

http://www.example.com/PHPJK/UserArea/Authenticate.php?sUName=&lt;/textarea&gt;'"><script>alert(document.cookie)</script>