The order cancellation function accepts an order identifier from the request and acts on that order without checking that the caller owns it. Any site visitor can set orders that are still awaiting payment to "canceled". This requires a page that contains the shop's order plugin. Orders that are already paid are not affected.

The payment notification endpoint for PayPal accepts incoming data without verifying that it comes from the payment provider. Any site visitor can overwrite the stored payment notification of an order that is still awaiting payment with arbitrary content. This requires a page that contains the shop's order plugin. Orders that are already paid are not affected.