pf overload for SMTP (was: Thousands of ssh probes)
john at starfire.mn.org
Fri Mar 5 16:35:09 UTC 2010
On Fri, Mar 05, 2010 at 04:01:32PM +0000, Matthew Seaman wrote:
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> On 05/03/2010 15:44:39, John wrote:
> > Maybe I'll have to learn how to do a VPN from FreeBSD....
> > One thought that occurs to me is that pf tables would provide a
> > direct API without having to hit a database.
> > I think I really like this. I may have to implement it for pf.
> > It should be really easy with CGI and calls to pfctl.
> There's already a mechanism whereby you can connect into a PF firewall
> and have it open up extra access for you, all controlled by ssh keys.
> See: http://www.openbsd.org/faq/pf/authpf.html
> Not only that, but you can dynamically block brute force attempts to
> crack SSH passwords using just PF -- no need to scan through auth.log or
> use an external database. You need something like this in pf.conf:
> table <ssh-bruteforce> persist
> [...near the top of the rules section...]
> block drop in log quick on $ext_if from <ssh-bruteforce>
> [...later in the rules section...]
> pass in on $ext_if proto tcp \
> from any to $ext_if port ssh \
> flags S/SA keep state \
> (max-src-conn-rate 3/30, overload <ssh-bruteforce> flush global)
> This adds IPs to the ssh-bruteforce table if there are too frequent
> attempts to connect from them (more than 3 within 30 seconds in this
> case) and so blocks all further access.
> You need to run a cron job to clear out old entries from the
> ssh-bruteforce table or it will grow continually over time:
> */12 * * * * /sbin/pfctl -t ssh-bruteforce -T expire 86400 >/dev/null 2>&1
Is there any reason one couldn't do something similar for SMTP? Maybe
a little wider sample window, like 10/300? Or would you end up blocking
too any things that you don't mean to block? Anyone played with this
john at starfire.MN.ORG
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