Hello i suggest block every outbound ports on your servers use ip_conntrack to allow servers to answer ESTABLISHED connections on your open ports (like 80 for a http server) botnets or trojan downloaders can simply run on any port a vulnerable script could be used to run a "wget ..." command that would use outbound tcp 80, which isnt in irc's port ranges, thats why you should simply block them all hth Maxime Ducharme Programmeur / Spécialiste en sécurité réseau ----- Original Message ----- From: "hbeaumont hbeaumont" <ahlist@xxxxxxxxx> To: <netfilter@xxxxxxxxxxxxxxxxxxx> Sent: Tuesday, August 02, 2005 11:41 AM Subject: blocking irc + botnets Can anyone help me with the proper method to block outgoing requests to botnets + irc? Or point me in the direction of searchable list archives (I could only find the non-searchable archives) or other FAQ that answers this? Problem: We have servers that could get infected via poorly wrote user scripts. I want to prevent these servers from being used as part of botnets or general connections to IRC (most scripts I run across seem to try to connect to IRC). I want to take the best preventative measures I can in case one of the machines would become infected or otherwise compromised. Also, interested in any other popular method of stopping general outgoing DOS attacks (rate limiting UDP perhaps? I'm not real up on the techniques used by the DOS'ers). I'm interested in the recommended rules to add to prevent this type of thing should it occur. Thanks.
