Firewall blocking issue port 0


we have serveral es440 with firmware we use the serial port a lot.
there are many hack attempts to port 0. which the modem allows to pass. we have tried to block port 0, and then tried to block all ports except the ones we use. in either case the modem makes the hackers connection to port 0. then the hacker tries to send data which eventually locks up the modem port. to correct this we have to reboot the modem.
I think this is a flaw in the firmware which does not block port 0
here is a partial log event
Nov 14 19:54:59 debug ALEOS_SERIAL_HMC: Socket 65535 IP: Port 0 Connection Manager state: 1
Nov 14 19:54:59 info ALEOS_SERIAL_HMC: Connect to IP: Port 0

need HELP! any ideas