auto-blackholing/blacklisting on multiple hacking attempts

[Olli Hauer]

> > Hi,
> > 
> > I'm running freebsd 7-RELEASE
> > 
> > I see this, for example, in my auth log:
> > 
> > May 15 02:00:39 www sshd[9180]: Invalid user web from 201.18.232.30
> > May 15 02:00:41 www sshd[9182]: Invalid user web from 201.18.232.30
...
> > May 15 02:01:43 www sshd[9248]: Invalid user apache from 201.18.232.30
> > May 15 02:01:45 www sshd[9250]: Invalid user apache from 201.18.232.30
> > May 15 02:01:47 www sshd[9252]: Invalid user apache from 201.18.232.30
> > 
> > I'd like it to be so that if an IP tries to connect to sshd more than
> > once in a 30 second period, that they are immediately blackholed.
> > Should I be using pf for this or would it be done better in some other
> > utility?
> > 
> 
> In pf you could write a rule like 
> 
> pass in quick on $ext_if proto tcp from any to $some_ip_address port 22
> flags S/SAFR keep state (max-src-conn 1, max-src-conn-rate 1/30,
> overload <ssh_hacks> flush global) 
> 
> you would have to have setup a table named <ssh_hacks> in your
> configuration and assign values to both $ext_if and $some_ip_address or
> replace them with whatever values work for you. 
> 
> This rule would track connections allowing a maximum of 1 connection per
> source IP address and would allow 1 connection to be initiated every 31
> seconds or longer, otherwise it would add the offending IP address to
> the <ssh_hacks> table and flush the global state table of all entries
> from the same source IP. 
> 
> You would have to have a rule in your configuration prior to this rule
> that would block traffic from source IP addresses in the ssh_hacks
> table. Depending on your policies this could be a block of all services
> or just ssh. Personally I use a rule like
> 
> block drop log quick from <ssh_hacks> 
> 
> but 
> 
> block drop log in quick proto tcp from <ssh_hacks> to any port 22 
> 
> would block ssh traffic from the offending IP to just ssh services on
> your network. 
> 
> Beware that you can lock yourself out of your servers very quickly with
> this if you do not have another rule allowing yourself access to your
> machines setup earlier in your configuration. 
> 

I have a nice script for my OpenBSD machines aviable, with some small changes it will work also on FreeBSD.

The script make usage of a special table <bf_ssh> dumps and compare the addresses with a run some minutes ago (cron job) and reports the ip's per mail with the help of GeoIP.
This reports make it easy to block big network ranges where you don't expect to travel ...

You can get the script here:
http://sorry.mine.nu/scripts/pftable_to_file.sh.txt

ps:
In the directoy is also an actual bf_ssh dump from one of my machines

regards,
 olli
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