Active Debug Code vulnerability in Mitsubishi Electric Corporation MELSEC WS Series WS0-GETH00200 Serial number 2310 **** and prior allows a remote unauthenticated attacker to bypass authentication and illegally log into the affected module by connecting to it via telnet which is hidden function and is enabled by default when shipped from the factory. As a result, a remote attacker with unauthorized login can reset the module, and if certain conditions are met, he/she can disclose or tamper with the module's configuration or rewrite the firmware.