Is NAT can provide some kind of protection?

Thu Jan 13 03:02:22 UTC 2011

In message <AANLkTikiXF_mbuo-osKPjSW98vn5_d5WZNUi_PL37sNG at mail.gmail.com>, William
 Herrin writes:
> On Wed, Jan 12, 2011 at 12:16 PM,  <Valdis.Kletnieks at vt.edu> wrote:
> > On Wed, 12 Jan 2011 12:04:01 EST, William Herrin said:
> >> In a client (rather than server) scenario, the picture is different.
> >> Depending on the specific "NAT" technology in use, the firewall may be
> >> incapable of selecting a target for unsolicited communications inbound
> >> from the public Internet. In fact, it may be theoretically impossible
> >> for it to do so. In those scenarios, the presence of NAT in the
> >> equation makes a large class of direct attacks on the interior host
> >> impractical, requiring the attacker to fall back on other methods like
> >> attempting to breach the firewall itself or indirectly polluting the
> >> responses to communication initiated by the internal host.
> >
> > Note that the presence of a firewall with a 'default deny' rule for inbou=
> nd
> > packets provides the same level of impracticality.
> 
> Hi Valdis,
> 
> There's actually a large difference between something that's
> impossible for a technology to do (even in theory), something that the
> technology has been programmed not to do and something that a
> technology is by default configured not to do.

Well ask the firewall vendor not to give you the knob to open it
up completely.

Note the CPE NAT boxes I've seen all have the ability to send
anything that isn't being NAT'd to a internal box so it isn't like
NAT boxes don't already have the flaw you are complaining about.
Usually it's labeled as DMZ host or something similar.

They also have the ability to send traffic for individual port to
particular boxes on the inside without it being initiated from the
inside.

Mark
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org