NivoCart through 2.5.1 Guest Order Invoice Disclosure via account/order/download

NivoCart through 2.5.1 contains a missing authorization vulnerability in the download() action of account/order that allows unauthenticated attackers to retrieve guest order invoices by supplying an order_id. Attackers can iterate the order_id parameter, which matches guest orders stored with customer_id 0, to disclose guest names, addresses, telephone numbers, emails, purchased items, and totals.