Re: Harnessing Service Discovery

[Toni Ruottu <toni.ruottu () iki fi>]

On Wed, 2008-11-26 at 16:05 -0700, David Fifield wrote:
> On Mon, Nov 24, 2008 at 08:18:19PM +0200, Toni Ruottu wrote:
> > The technologies can also be combined to improved port scanners. Port
> > scanners can use service discovery as a source of information regarding
> > open ports. In some cases a port scanner could avoid sending any
> > packages, if a discovery service already revealed enough information
> > regarding the interesting ports.
> >
> > Service discovery can also be used to get a list of target hosts/ports
> > to scan. In a local network, port scanning the advertised hosts could be
> > used to verify that the services are actually running, while in a
> > foreign network, the advertisements might reveal interesting nodes to
> > scan (or honey pots used for port scan detection!).
> >
> > ------------------------------------------------------------------------
> >
> > To get my hands dirty on the subject, I wrote a simple script which uses
> > Avahi Bonjour implementation to produce an Nmap compatible XML-file that
> > can be opened in Zenmap for inspection. I have attached the script to
> > this email for your convenience, but I also created a Bazaar repository
> > to Launchpad.net for those of you who'd prefer getting a branch instead.
>
> Hi Toni. This is a neat idea. I checked out your branch and ran the
> program. There's a Mac OS X host on the local LAN. I attached the
> resulting bonmap-david.xml.

Looking at it now.

> It found ports 22 and 5900 on the Mac, but missed 88 which was also
> open. 

There is no guarantee of finding every open port. Only the advertised
ones.

> The local host is not running any kind of Zeroconf but port 9 on localhost
> was marked up, which it is not.

Many hosts seem to be advertising port 9. Port 9 is reserved for discard
service, which is probably the most simple protocol running on top of
TCP and UDP (see RFC863 [1]). However, I have seen none of the hosts
actually implementing the protocol. Maybe it would be appropriate for
Bonmap to filter out all results regarding port 9 and using that data
only to mark that the host is up when on other ports were discovered.

[1] http://www.faqs.org/rfcs/rfc863.html

(btw: If you installed Avahi, you are running Zeroconf by now. ;-)

> (I noticed the output doesn't
> differentiate TCP and UDP ports. Is that information available?)

No, it is not. I think this is simply because port numbers are assigned
to services without differentiating between different transports. It is
then up to the service to decide whether it wants to use TCP, UDP or
both. It would be possible to build a database, which lists transports
certain services typically use and relying on that information for the
scan.

> This technique of an external program generating Nmap XML can be very
> powerful when combined with Zenmap's scan aggregation. You could do a
> normal port scan and then supplement the results by loading a Bonmap
> file.

I have to try that out. I was hoping people would be creative.

> This is an interesting area of study. I admit to being almost totally
> ignorant about Zeroconf/Bonjour/Avahi, but networks are changing all the
> time so we'll need tools to deal with all the new developments.

Indeed :-)


  --Toni



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