A vulnerability was identified in rathena FluxCP up to 98cd4b8fd83228c11b36fb3d097b8e0f7c105a8d. This issue affects the function verifyiprange of the file lib/Flux/PaymentNotifyRequest.php of the component PayPal IPN Handler. The manipulation of the argument X-Real-IP leads to origin validation error. The attack is possible to be carried out remotely. The exploit is publicly available and might be used. The vendor was contacted early about this disclosure but did not respond in any way.