ubuntu-devel Digest, Vol 23, Issue 16

Nathan Sutton nathan.sutton at gmail.com
Tue Jul 4 22:48:31 BST 2006

> On 7/4/06, Scott James Remnant <scott at ubuntu.com> wrote:
> > > There should be no exception: there should be no open ports by default.
> > >
> > This isn't actually entirely true; we currently have two open ports by
> > default:
> >
> > If you're on a network with DHCP, the DHCP client listens on UDP port 68
> > to receive responses from the DHCP server.
> >
> > And every time you make a DNS query, a UDP port is opened to receive the
> > response from the DNS server.
> Both of these are examples of getting replies to queries sent out by the
> system, so they don't count, really.
> - Dan

Ahh, but UDP doesn't maintain state, except at higher levels in the
OSI model.  This can be exploited for ARP poisoning attacks and DoS,
so these examples do count.


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