On Tue, Aug 25, 2009 at 2:43 PM, Bill Moran <wmo...@potentialtech.com>wrote:
> In response to Adam Vande More <amvandem...@gmail.com>:
>
> > On Tue, Aug 25, 2009 at 12:06 PM, Bill Moran <wmo...@potentialtech.com
> >wrote:
> >
> > > In response to Adam Vande More <amvandem...@gmail.com>:
> > >
> > > > On Tue, Aug 25, 2009 at 11:05 AM, Bill Moran <
> wmo...@potentialtech.com
> > > >wrote:
> > > >
> > > > > In response to Paul Schmehl <pschmehl_li...@tx.rr.com>:
> > > > >
> > > > > > --On Tuesday, August 25, 2009 08:30:17 -0500 Colin Brace <
> c...@lim.nl>
> > > > > wrote:
> > > > > >
> > > > > > > Bill Moran wrote:
> > > > > > >>
> > > > > > >> You can add an ipfw rule to prevent the script from calling
> home,
> > > > > which
> > > > > > >> will effectively render it neutered until you can track down
> and
> > > > > actually
> > > > > > >> _fix_ the problem.
> > > > > > >
> > > > > > > Mike Bristow above wrote: "The script is talking to
> 94.102.51.57 on
> > > > > port
> > > > > > > 7000". OK, so I how do I know what port the script is using for
> > > > > outgoing
> > > > > > > traffic on MY box? 7000 is the remote host port, right?
> > > > > > >
> > > > > > > FWIW, here are my core PF lines:
> > > > > > >
> > > > > > > pass out quick on $ext_if proto 41
> > > > > > > pass out quick on gif0 inet6
> > > > > > > pass in quick on gif0 inet6 proto icmp6
> > > > > > > block in log
> > > > > > >
> > > > > > > That is to say: nothing is allowed in unless explicitly allowed
> > > > > > > Everything allowed out.
> > > > > > > (plus some ipv6 stuff I was testing with a tunnel)
> > > > > > >
> > > > > >
> > > > > > The problem with blocking outbound ports is that it breaks things
> in
> > > odd
> > > > > ways.
> > > > > > For example, your mail server listens on port 25 (and possibly
> 465 as
> > > > > well) but
> > > > > > it communicates with connecting clients on whatever ethereal port
> the
> > > > > client
> > > > > > decided to use. If the port the client selects happens to be in
> a
> > > range
> > > > > that
> > > > > > you are blocking, communication will be impossible and the client
> > > will
> > > > > report
> > > > > > that your mail server is non-responsive.
> > > > >
> > > > > You're doing it wrong. Block on the destination port _only_ and
> you
> > > don't
> > > > > care about the ephemeral ports.
> > > >
> > > > What ports would you block then when you're trying to run a
> webserver?
> > >
> > > My point (which is presented in examples below) is that you block
> > > everything
> > > and only allow what is needed (usually only dns and ntp, possibly smtp
> if
> > > the web server needs to send mail)
> > >
> > > That single statement above was directed specifically at the comment
> about
> > > it being impossible to predict (and thus block) ephemeral source ports.
> > > He's
> > > right about that, and that's why filtering on the destination port is
> the
> > > more common practice.
> > >
> > > Of course, that caused me to create an email that seems to contradict
> > > itself, if you don't notice that it's two answers to two different
> > > comments.
> >
> > My point was that it's unfeasible to block by destination point. You can
> > only block by destination port if it's a known quantity, and the
> destination
> > port is ephemeral in the question I posed(which what the OP had an issue
> > with).
>
> Please read the entire email before you respond. My last example below
> demonstrates how to do what you call "unfeasible".
>
> > > > > > It's much easier to block outgoing ports for services you *don't*
> > > want to
> > > > > > offer, but, if the service isn't running anyway, blocking the
> port is
> > > > > > non-productive.
> > > > >
> > > > > You're obviously misunderstanding me completely. Your not blocking
> > > > > incoming
> > > > > connections, your preventing outgoing ones, which means there _is_
> no
> > > > > service running on your local machine.
> > > > >
> > > > > For example, a server that is _only_ web (with SSH for admin) could
> > > have
> > > > > a ruleset like:
> > > > >
> > > > > pass in quick on $ext_if proto tcp from any to me port
> {25,587,465,22}
> > > keep
> > > > > state
> > > > > pass out quick on $ext_if proto tcp from me to any port {25} keep
> state
> > > > > pass out quick on $ext_if proto upd from me to any port {53,123}
> keep
> > > state
> > > > > block all
> > > > >
> > > > > (note that's only an example, there may be some fine points I'm
> > > missing)
> > > > >
> > > > > One thing that had not yet been mentioned when I posted my earlier
> > > comment,
> > > > > is that this system is a combination firewall/web server. That
> makes
> > > the
> > > > > rules more complicated, but the setup is still possible:
> > > > >
> > > > > pass in quick on $ext_if proto tcp from any to me port {80} keep
> state
> > > > > pass out quick on $ext_if proto upd from me to any port {53,123}
> keep
> > > state
> > > > > pass out quick on $ext_if from $internal_network to any all keep
> state
> > > > > block all
> > > > >
> > > > > Which allows limited outgoing traffic originating from the box
> itself,
> > > > > but allows unlimited outgoing traffic from systems on
> > > $internal_network.
> > > > >
> > > > > I've done this with great success. In fact, I had a fun time where
> a
> > > > > client in question was infected with viruses out the wazoo, but the
> > > > > viruses never spread off their local network because I only allowed
> > > > > SMTP traffic to their SMTP relay, which required SMTP auth (thus
> the
> > > > > viruses couldn't send mail)
> > > > >
> > > > >
> > > >
> > > >
> > > > --
> > > > Adam Vande More
> > > > _______________________________________________
> > > > freebsd-questions@freebsd.org mailing list
> > > > http://lists.freebsd.org/mailman/listinfo/freebsd-questions
> > > > To unsubscribe, send any mail to "
> > > freebsd-questions-unsubscr...@freebsd.org"
> > >
> > >
> > > --
> > > Bill Moran
> > > http://www.potentialtech.com
> > > http://people.collaborativefusion.com/~wmoran/<http://people.collaborativefusion.com/%7Ewmoran/>
> <http://people.collaborativefusion.com/%7Ewmoran/>
> > >
> >
> >
> >
> > --
> > Adam Vande More
>
> You said block by destination port. What you presented is not this,
although it gives give a functional environment of it. Sorry for the
pedantic pursuit here, but IMO terminology is important here.
--
Adam Vande More
_______________________________________________
freebsd-questions@freebsd.org mailing list
http://lists.freebsd.org/mailman/listinfo/freebsd-questions
To unsubscribe, send any mail to "freebsd-questions-unsubscr...@freebsd.org"
