From The Hacker News
Does anyone know of a linux tool that can immediately ban an IP address if they try to log in to ssh with specific user names? I see a ton of attempts in my logs for names like fax, mysql, admin, and of course root. Fail2ban only works if the same IP makes repeated attempts but I’m betting if I could generate a list from these failed attempts it would probably correlate with standard blocklists of compromised hosts. For that matter, is there a way to use an RBL to limit addresses that ssh will even accept? Of course none of these attempts have a chance of logging in, but it would still be nice to further limit my exposure for any future attacks.
I think is better to not use an standard port and using fail2ban at the same time to avoid automated attacks. If you manage to implent what you are looking for, you are potentially telling an stacker which accounts exist and which not, allowing him to do an easier brute force attack. A typical attacker using a botnet will not be stopped by a single IP being baned, and as son as an IP is banned he will know that this account doesn’t exists. Another option is enabling port knocking.
Normally when an ssh login fails, it does so after the password attempt so no clue is given about which step failed. I would assume any type of RBL blocking would do the same, along with any available plugins that would ban based on a given username attempt?
One good thing though… I just realized fail2ban actually has a rule for blocking based on invalid user names, so I need to update my settings to make use of that filter. That will likely take care of the large number of attempts I’m seeing since I do see a number of IPs being used over and over.
Eh, those attempts are just noise anyway. Use proper pubkey auth instead of normal passwords and you’ll be fine. Any key size is probably enough to prevent successful bruteforce attacks. Anything above 2048 and there’s basically no chance for them to guess right within several years of constant trying. Most bots move along quickly as well, they try their predefined list of (common usernames) x (common passwords) and that’s it.
Install endlessh, an ssh tar pit, if you want to make their lives a little more annoying. Use a non-standard port if your OCD can’t stand the slowly filling auth attempt logs.
