Payment Gateway for Telcell < 2.0.5 - Unauthenticated Payment Confirmation Forgery via Empty-Default Merchant Secret

Description

The plugin does not verify the authenticity of incoming payment notifications, because the secret used to sign them is empty by default, allowing unauthenticated attackers to forge a valid notification and mark arbitrary WooCommerce orders as paid. The same handler also marks an attacker-chosen order as failed when given an invalid signature.