Calculated Fields Form <= 5.5.1.3 - Reflected DOM-Based Cross-Site Scripting via 'x' URL Query Parameter via Text Area Predefined Value

The Calculated Fields Form – AI Form Builder for WordPress – Contact, Payment, Quote, Quiz & More plugin for WordPress is vulnerable to Reflected DOM-Based Cross-Site Scripting via the 'x (attacker-chosen name matching the form's url.<name> predefined value)' parameter in all versions up to, and including, 5.5.1.3 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. Exploitation requires that the targeted form has a Text Area field configured with a 'url.<name>' Predefined Value and predefinedClick disabled, which is a documented and commonly used plugin feature.