In response to Adam Vande More <amvandem...@gmail.com>:

> On Wed, Aug 26, 2009 at 7:11 AM, Bill Moran <wmo...@potentialtech.com>wrote:
> 
> > Adam Vande More <amvandem...@gmail.com> wrote:
> > >
> > > 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/>
> > > > <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.
> >
> > Both of my examples are filtering based on destination port.  In reviewing
> > this thread, you make the statement "destination ports are ephemeral" which
> > is wrong.  I can only assume that your understanding of IP port usage is
> > wrong or incomplete.
> >
> 
> blocking destination port != keep state

Why not?  Because you said so?

> and destination port are certainly ephemeral simply depends on pov.  Your
> original statement indicated blocking by port at egress was the way to go.
> Your example did no such thing, it tracked state which is completely
> different from both a functional and technical standpoint.

This paragraph serves to further convince me that you are getting
concepts confused.  I see no reason for me to continue discussing this.

-- 
Bill Moran
http://www.potentialtech.com
http://people.collaborativefusion.com/~wmoran/
_______________________________________________
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"

Reply via email to