SKT PayPal for WooCommerce <= 1.4 - Unauthenticated Payment Bypass

The SKT PayPal for WooCommerce plugin for WordPress is vulnerable to Payment Bypass in all versions up to, and including, 1.4. This is due to the plugin only enforcing client side controls instead of server-side controls when processing payments. This makes it possible for unauthenticated attackers to make confirmed purchases without actually paying for them.