PAYable IPG < 1.3.1 - Unauthenticated Order Payment Forgery via Unsigned Callback

The Payable Payment Gateway for WooCommerce WordPress plugin before 1.3.1 does not verify the authenticity of an incoming payment notification before marking a WooCommerce order paid or failed, allowing unauthenticated attackers to change the payment status of any order in the store regardless of the payment method it was placed with.