Klarna for WooCommerce <= 4.13.3 - Missing Authorization to Unauthenticated Sensitive Information Disclosure via 'order-pay' Endpoint

The Klarna for WooCommerce plugin for WordPress is vulnerable to authorization bypass in all versions up to, and including, 4.13.3 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 access any order's secret order_key and full billing and shipping PII — including first name, last name, email address, phone number, street address, postcode, city, region, and country — emitted inline as the klarna_payments_params JavaScript variable, enabling full store-wide order enumeration. Because WooCommerce order IDs are sequential integers and no order_key or authenticated session is required, every order in the store can be trivially enumerated with sequential GET requests to the order-pay endpoint.