iPaymu Payment Gateway for WooCommerce <= 2.0.2 - Missing Authentication to Unauthenticated Payment Bypass and Order Information Disclosure

The iPaymu Payment Gateway for WooCommerce plugin for WordPress is vulnerable to Missing Authentication in all versions up to, and including, 2.0.2 via the 'check_ipaymu_response' function. This is due to the plugin not validating webhook request authenticity through signature verification or origin checks. This makes it possible for unauthenticated attackers to mark WooCommerce orders as paid by sending crafted POST requests to the webhook endpoint without any payment occurring, as well as enumerate order IDs and obtain valid order keys via GET requests, exposing customer order PII including names, addresses, and purchased products.