On October 23, 2007 07:30:25 pm david l goodrich wrote:
quoted text
> On Tue, Oct 23, 2007 at 02:55:41PM -0700, Rob wrote:
> > On 10/23/07, david l goodrich <dlg@dsrw.org> wrote:
> > > Nobody?  Sad, it's still doing it.
> > >
> > > On Sun, Oct 21, 2007 at 02:22:43PM -0500, david l goodrich wrote:
> > > > I've set up a max-src-conn-rate rule on my gateway router to
> > > > mitigate brute-force ssh attacks.  This router protects a /28
> > > > subnet, 25.108.82.80/28.
> > > >
> > > > The relevant rules:
> > > >
> > > > # pfctl -sr | grep attack
> > > > block drop in log quick proto tcp from <sshd_attackers> to any
> > > > pass in log proto tcp from any to any port = ssh keep state
> > > > (source-track rule, max-src-conn-rate 3/30, overload
> > > > <sshd_attackers> flush global, src.track 30)
> > > > #
> > > >
> > > > What the three columns of output in the below tcpdump output are:
> > > > timestamp, rule action, and target host.  As you can tell from
> > > > the tcpdump command, the sending host is the same in all cases,
> > > > 208.53.147.204
> >
> > I'm not a pf newbie by any means, but I'm not really qualified to
> > answer questions about it either. That said, I don't usually use an
> > '=' sign in my pf rules, and the pf faq doesn't list that as one of
> > the accepted operators for the port range
> > (http://www.openbsd.org/faq/pf/filter.html). If the rule wasn't being
> > parsed correctly, it would cause the behavior you're seeing. Try,
>
> I don't have an = sign in my rule, either, i have it in pf.conf as:
>
> pass in log proto tcp from any to any port ssh \
>         keep state (max-src-conn-rate 3/30, \
>                         overload <sshd_attackers> flush global)
>
> but when i look at my rules with pfctl -sr it shows the =.
>
> > block in log quick proto tcp port ssh keep state \
> >    (source-track rule, max-src-conn-rate 3 / 30 overload
> > <sshd_attackers>, src.track 30)
>
> I want to pass ssh traffic by default, so a block rule won't be
> terribly helpful.
>
> > Note that I wouldn't use a flush global directive for a rule like
> > this, because it can lead to a neat DoS where somebody can spoof one
> > of your own IP addresses and shut down any ssh sessions you have
> > active.
> >
> > Here's a working sample from my own currently active pf file:
> >
> > pass in on $ext proto tcp to <server6> port smtp keep state \
> >    (max-src-conn 15 max-src-conn-rate 10 / 45 overload <smtp-overload>) \
> >    queue 6smtp
>
> Mine's pretty similar, if a bit more verbose.  And I don't use
> max-src-conn or queueing.
>   --david
>
> > (FYI, the smtp-overload table moves traffic to a queue that simply
> > throttles the connections a little.)
> >
> > - R.
>
> !DSPAM:1,471e93c5217372013633067!

I tried various combinations on my test machine and noticed the following 
pattern. Setting the max-src-conn to be twice the max-src-conn-rate seems to 
work better at stopping brute-force SSH attempts. Probably there is no 
rational basis for this observation and there must be some other explanation. 
I did try a few combinations and it seemed to have had a positive impact in 
getting the IP address to the sshd_attackers table at the right 
max-src-conn-rate.

So I am wondering if

pass in log proto tcp from any to any port ssh keep state (max-src-conn 6  
max-src-conn-rate 3/30, overload <sshd_attackers> flush global)

would be an appropriate thing for you to try.

Anyways, hope this helps in some way.

-- 
Vijay Sankar, M.Eng., P.Eng.
President & CEO
ForeTell Technologies Limited
59 Flamingo Avenue, Winnipeg, MB Canada R3J 0X6
Phone: +1 204 885 9535, E-Mail: vsankar@foretell.ca