FormCraft <= 3.9.14 - Unauthenticated Stored Cross-Site Scripting via Matrix Field Sub-Parameters

Summary

The FormCraft plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the '[parameter name]' parameter in all versions up to, and including, 3.9.14 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. The exploit chain combines a server-side gap — where composite matrix sub-field keys such as field2_0 and field2_1 are never passed through the sanitization loop and are stored raw via $wpdb->insert() — with a client-side gap where DOMPurify is only invoked when typeof field.value === 'string', but matrix values arrive from the server as arrays, bypassing the check before being mapped to strings and injected into the DOM. Additionally, the same sink is reachable via a second attack vector: array-typed field values are passed through htmlentities() on submission but later reversed by html_entity_decode() at formcraft-main.php:2608 and :2122, restoring the malicious payload before storage and rendering.