Ostin654 JustClick registration plugin vulnerabilities

The JustClick registration plugin for WordPress is vulnerable to Reflected Cross-Site Scripting in all versions up to, and including, 0.1. This is due to insufficient input sanitization and output escaping on the `PHP_SELF` server variable. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that execute if they can successfully trick a user into performing an action such as clicking on a link.