SSH scans vs connection ratelimiting

[Pieter de Boer]

Constantine A. Murenin wrote:

>> So, my question is: Does anyone know how this particular attack works
>> and if there's a way to stop this? If my theory is sound and OpenSSH
>> does not have provisions to limit the authentication requests per TCP
>> session, I'd find that an inadequacy in OpenSSH, but I'm probably
>> missing something here :)

> This is just one thread that I've found now, called "is there a way to
> block sshd trolling?":
> http://arkiv.openbsd.nu/?ml=openbsd-misc&a=0&t=1325006.
> 
> Most of these attacks come from compromised Linux hosts, so if you use
> pf(4), you could easily block access to ssh port from any Linux
> machine, and then you're mostly covered. :) See
> http://arkiv.openbsd.nu/?ml=openbsd-misc&a=0&m=1332409.
I'm not so much searching for a solution to the 'problem', but rather 
want to know why ratelimiting apparantly doesn't work for some of the 
scans. I see IP addresses being blocked just fine by the pf rule due to 
  scans, but also see some other scans still succeed. Ratelimiting is 
one of the few solutions I can agree with, and it should simply work.

Perhaps I should try running a tcpdump for a few days again to get a 
packet trace of such a 'succeeding' scan. Might show what's going on..

-- 
Pieter