PayHere Payment Gateway 2.4.0 - 2.4.5 - Unauthenticated Payment Bypass via Unverified Payment Notification

The PayHere Payment Gateway WordPress plugin from 2.4.0 through 2.4.5 does not verify the authenticity of payment notifications when the merchant secret is unset, which is the default state, allowing unauthenticated attackers to forge a payment confirmation and mark any order as paid without payment.