Cross-site scripting (XSS) vulnerability in wp-register.php in WordPress 2.0 allows remote attackers to inject arbitrary web script or HTML via the user_login parameter.
https://exchange.xforce.ibmcloud.com/vulnerabilities/36742
http://www.securityfocus.com/archive/1/480327/100/0/threaded
http://securityreason.com/securityalert/3175
http://blogsecurity.net/wordpress/2-vanilla-xss-on-wordpress-wp-registerphp/