The Payment Integration Wompi WordPress plugin through 4.0.1 does not verify the authenticity of...

The Payment Integration Wompi WordPress plugin through 4.0.1 does not verify the authenticity of incoming payment notifications on a stock install, because the callback's checksum is keyed on a merchant secret that is empty until it is manually configured, allowing an unauthenticated attacker to forge a notification and mark an arbitrary order as paid.