Posted on February 20, 2013 9:46 am

SSH Password Gropers Are Now Trying High Ports

from the for-higher-love dept.

“You thought you had successfully avoided the tiresome password guessing bots groping at your SSH service by moving the service to a non-standard port? It seems security by obscurity has lost the game once more. We’re now seeing ssh bruteforce attempts hitting other ports too, Peter Hansteen writes in his latest column.” For others keeping track, have you seen many such attempts?

I’ve been using key based authentication for ssh for years. I just moved the service to a high port to get rid of all the script kiddy password guessing attempts that were clogging my log file. I also added a “throttle” in iptables:

# Block brute force attacks
# Drop repeated ssh connection attempts within 20 seconds interval
-A INPUT -p tcp -m tcp -m state -m recent -i eth1 --dport 22222 --state NEW -j DROP --rcheck --seconds 20 --name THROTTLE --rsource

# Accept ssh connection if not attempted within past 20 sec.
-A INPUT -p tcp -m tcp -m state -m recent -i eth1 --dport 22222 --state NEW -j ACCEPT --set --name THROTTLE --rsource

It just cuts down on the noise. I used the same technique back when people were doing the DNS cache poisoning attacks to limit how many hits my DNS could get from the same source (first query should update the cache in a legitimate site’s DNS so no reason why I should get repeated hits from the same site).