An exploitable denial-of-service vulnerability exists in the iocheckd service "I/O-Check" functionality of WAGO PFC 200 Firmware versions 03.01.07(13) and 03.00.39(12), and WAGO PFC100 Firmware version 03.00.39(12). A single packet can cause a denial of service and weaken credentials resulting in the default documented credentials being applied to the device. An attacker can send an unauthenticated packet to trigger this vulnerability.