Blocking SSH Brute-Force Attacks: What Am I Doing Wrong?

Eric heli at
Tue Nov 14 20:52:52 UTC 2006

Erik Norgaard wrote:
> Leo L. Schwab wrote:
>> On Mon, Nov 13, 2006 at 09:16:35PM +0100, Erik Norgaard wrote:
>>> Honestly, I wouldn't worry about it: review your config and make some 
>>> simple choices to reduce the noise, see this article:
>>     But I rather thought that was the point of 'bruteblock' -- it
>> reduces the noise by blackholing the offending IPs for an hour or so.  
>> This
>> blackholing doesn't appear to be happening, and I don't understand why.
>>     Could it be a permission problem -- syslog doesn't have permission
>> to change the firewall rules?
> I wouldn't worry about "bruteblock" - try create a perl script and see 
> if you can see a system in the attacks: Do the same host come back? If 
> so does it continue from where it left?
> The annoyance of these brute force attacks is that your log is larger 
> that it would be without them.
> That is unless ofcourse you have made yourself vulnerable!
> - do you use bad passwords?
> - do you allow root login?
> - have you disabled system accounts?
> If the answers are no, no and yes, then you can largely ignore. For more 
> on this - read the linked article, read the old thread.
> Cheers, Erik

jumping into this thread late, but denyhosts works great and also does a 
distributed thing where, if you opt in, you can get updates from other 
people who run denyhosts. These are then added to your deny list and if 
your box is scanned the attempts will be blocked.  think if it like a 
spamhaus list for SSH brute force attacks. it works well.

in short:

1. use denyhosts
2. do not use password based authentication for ssh. rather, use keys 
that are password protected
3. never allow root ssh logins

and everything should be swell


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