PhonePe Payment Solutions < 3.1.0 - Unauthenticated Payment Bypass via Forged Callback

Description

The plugin does not properly verify the authenticity of incoming payment callbacks: the secret used to validate the callback signature is empty on sites configured through the current setup flow, so the expected signature reduces to an unkeyed hash of the request body that anyone can compute. This allows unauthenticated attackers to forge a payment-success notification and mark unpaid WooCommerce orders as paid without any payment being made.