The WP-Members Membership Plugin plugin for WordPress is vulnerable to Reflected Cross-Site Scripting via URL Query String in all versions up to, and including, 3.5.6 due to insufficient input sanitization and output escaping. 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. Successful exploitation requires the victim to first visit the attacker-crafted URL and then click the Terms of Service link rendered on the resulting registration page.