Avada (Fusion) Builder <= 3.15.1 - Authenticated (Subscriber+) Sensitive Information Exposure via Insecure Direct Object Reference

The Avada (Fusion) Builder plugin for WordPress is vulnerable to Sensitive Information Exposure in all versions up to, and including, 3.15.1. This is due to the plugin's `fusion_get_post_custom_field()` function failing to validate whether metadata keys are protected (underscore-prefixed). This makes it possible for authenticated attackers, with Subscriber-level access and above, to extract protected post metadata fields that should not be publicly accessible via the Dynamic Data feature's `post_custom_field` parameter.