Eventin < 4.1.24 - Unauthenticated Payment Bypass via Stripe and PayPal Cross-Order Transaction Replay

The Eventin WordPress plugin before 4.1.24 does not verify that a completed payment corresponds to the order it is applied to, confirming only that the payment gateway reports the transaction as successful, not its amount, currency, or which order it belongs to, allowing unauthenticated visitors to mark unpaid orders of any value as paid by replaying the transaction of a single genuine low-value payment.