Themify Builder < 7.8.1 - Missing Authorization to Unauthenticated Arbitrary Builder Data Modification via 'tb_update_old_data' AJAX Action

Description

The Themify Builder plugin for WordPress is vulnerable to authorization bypass in all versions up to, and including, 7.8.0. This is due to the plugin not properly verifying that a user is authorized to perform an action. This makes it possible for unauthenticated attackers to modify the stored Themify Builder styling data (padding and margin properties) of arbitrary posts, including private and draft posts, by supplying an attacker-controlled post ID and JSON styling payload. The nonce required by the handler is automatically emitted to all frontend pages rendered by the builder via wp_localize_script, meaning any unauthenticated visitor can trivially retrieve a valid nonce from page source and satisfy the only access control in place.