All udp ports open,,,, WHAT HAVE I DONE WRONG ?

[spyce69]

Hello here,

Hope somebody can help me out,
I am running a linux firewall solution, RH 7.0 with PMFirewall, Sendmail 8.11.0.
It's configured with an Internet IP doing NAT for the internal workstations, Sendmail is rerouting mail to an internal mail server, This all works great,
HOWEVER i am not sure if the firewall is doing a complete job,
When i run a port scan on the external IP, the only tcp port open is 25 which is needed for my mailserver, but ALL the udp ports seem to be open, I have a feeling this is a seriuos problem, Don't most trojans only use udp ?????
What else could get in ?
Hope Somebody Can adivse ....

Thanks

 

[GoldenEternity]

nmap assumes that a udp port is open if it does not receive an icmp port unreachable reply. So if you are dropping connections, it won't kick back any response, and thus nmap will assume everything is open.