The Casso Flow WordPress plugin before 4.2.0 does not properly authenticate incoming bank-transfer payment notifications, as the token used to verify them is empty on a default installation, allowing unauthenticated attackers to forge a notification and mark any pending WooCommerce order as paid, regardless of its payment method.
https://wpscan.com/vulnerability/2056019e-22bf-4ba1-9b3b-239a369f0219/