The JetFormBuilder — Dynamic Blocks Form Builder plugin for WordPress is vulnerable to Reflected DOM-Based Cross-Site Scripting via the '<attacker-chosen query var name matching the preset's query_var setting>' parameter in all versions up to, and including, 3.6.6 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. This is only exploitable on pages embedding a form that has a text field configured with a query_var Dynamic Preset and a data-jfb-macro or JFB_FIELD:: macro reference targeting that field, both of which are standard, documented plugin features.