I see many entries in /var/log/secure similar to these:
. . . /var/log/secure.1:Dec 31 08:00:55 gway01 sshd[7220]: Received disconnect from 93.89.144.31: 11: Bye Bye /var/log/secure.1:Dec 31 08:00:58 gway01 sshd[7221]: Failed password for root from 93.89.144.31 port 60100 ssh2 /var/log/secure.1:Dec 31 08:00:58 gway01 sshd[7222]: Received disconnect from 93.89.144.31: 11: Bye Bye /var/log/secure.1:Dec 31 08:01:02 gway01 sshd[7223]: Failed password for root from 93.89.144.31 port 60962 ssh2 /var/log/secure.1:Dec 31 08:01:02 gway01 sshd[7224]: Received disconnect from 93.89.144.31: 11: Bye Bye /var/log/secure.1:Dec 31 08:01:05 gway01 sshd[7227]: Failed password for root from 93.89.144.31 port 33612 ssh2 /var/log/secure.1:Dec 31 08:01:05 gway01 sshd[7228]: Received disconnect from 93.89.144.31: 11: Bye Bye /var/log/secure.1:Dec 31 08:01:09 gway01 sshd[7229]: Failed password for root from 93.89.144.31 port 34504 ssh2 . . .
As you can see, the ports are not those associated with the service requested. SSHD is configured to listen on the standard port (22) and only on a single IP address that is supposed to be reachable only from the internal network (this is a multi-homed system configured as a gateway).
These are getting through the brute force filters because the attempts are directed against unchecked ports. I suspect that these represent no immediate danger to our systems because there are no active services on any of the ports and because we have a guillotine rule at the end of our INPUT chain. The firewall is configured to only allow connections to specified ports and to drop any new connection attempts to all the others.
My confusion is over why these things are making it into the logs at all when sshd does not listen on those ports and the ports themselves are supposed to inaccessible through the firewall. There presence inoculates a doubt in my mind that things are properly configured.
I would appreciate any insight as to why these attempts are nonetheless logged by sshd.