Cost Calculator Builder < 3.6.10 - Missing Authorization to Unauthenticated Payment Status Bypass

Description

The Cost Calculator Builder plugin for WordPress is vulnerable to Unauthenticated Payment Status Bypass in all versions up to, and including, 3.6.9 only when used in combination with Cost Calculator Builder PRO. This is due to the complete_payment AJAX action being registered via wp_ajax_nopriv, making it accessible to unauthenticated users, and the complete() function only verifying a nonce without checking user capabilities or order ownership. Since nonces are exposed to all visitors via window.ccb_nonces in the page source, any unauthenticated attacker can mark any order's payment status as "completed" without actual payment.