WAGO: Series 750-3x/-8x prone to MODBUS server DoS

An attacker can crash or freeze your WAGO controller by overwhelming its MODBUS port with specially crafted packets, disrupting whatever process it controls—whether that's HVAC, water treatment, or electrical distribution—until the device is manually rebooted.

Water utilities, municipal electric systems, building automation operators, and other facility managers running WAGO Series 750-3x/-8x controllers or field bus couplers with BACnet/IP, EtherNet/IP, or MODBUS TCP should assess this risk. These controllers commonly manage HVAC, water treatment, pump sequencing, electrical switchgear, and other critical plant functions.

An attacker sends malformed MODBUS TCP packets to port 502 of a vulnerable WAGO controller. Each packet claims to start a new connection but does not complete it properly. The controller allocates memory for each incomplete connection but fails to release it when the attacker abandons the connection. After enough incomplete connections, the controller runs out of memory and stops responding to legitimate MODBUS requests or stops operation entirely.