The Newtec Celox UHD (models: CELOXA504, CELOXA820) running firmware version celox-21.6.13 is vulnerable to an authentication bypass. An attacker can exploit this issue by modifying intercepted responses from the /celoxservice endpoint. By injecting a forged response body during the loginWithUserName flow, the attacker can gain Superuser or Operator access without providing valid credentials.