Remote diagnostic systems, support diagnostic communication by having the capability of sending diagnostic requests to a vehicle and receiving diagnostic responses from a vehicle. Diagnostic communication includes but is not limited to the services that are specified in SAE J1979, SAE J1939 or ISO 14229 (UDS). Diagnostic communication utilizes the standard in-vehicle network, which is usually CAN. Any unauthorized access to the in-vehicle network poses a security vulnerability. Such vulnerabilities can severely harm the functional safety, thus causing damage to the vehicle, machine or – even worse – to life and health of the driver, passengers or operators. This paper describes the architecture of a system for remote diagnostics, its security vulnerability and measures to prevent unauthorized access to the in-vehicle network.