The Sadad QA Payment WordPress plugin through 1.28 does not correctly verify the authenticity of...

The Sadad QA Payment WordPress plugin through 1.28 does not correctly verify the authenticity of incoming payment notifications, as the verification is keyed on a merchant secret that is empty by default and the rest of the signed data is attacker-controlled, allowing unauthenticated attackers to forge a valid confirmation and mark orders as paid without payment.