The PayDunya WooCommerce Payment Gateway WordPress plugin through 1.1.6 does not verify the authenticity of incoming payment notifications and, until the gateway is configured, authenticates them with a value derived from an empty secret that anyone can compute, allowing unauthenticated attackers to mark arbitrary WooCommerce orders as paid and completed.
The product does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data.