Interesting paper by Steve Bellovin - Worm propagation in a v6 internet

Mark Andrews Mark_Andrews at
Wed Feb 15 05:00:41 UTC 2006

> On Wed, 15 Feb 2006, Mark Andrews wrote:
> > 	I suggest that you re-read RFC 1034 and RFC 1035.  A empty
> > 	node returns NOERROR.  A non-existant node returns NXDOMAIN
> > 	(Name Error).
> Right.  This means depth-first walk, which will reduce the *possible*
> address space to probe, but that is the antithesis of traditional scanning
> (which is often at least partly stochastic).  To a worm, the benefit of
> stochastic scanning is that no collaboration between infected hosts is
> needed; but with a walking traversal, you have to have some kind of
> statekeeping if the walk search is not intended to take ~forever.
> I can see this vector as being useful for scanning within some specific
> organization's subnet, but even then, you'll need some kind of collaboration
> with NDP solicitations for most internal setups.  Stateless autoconfig, for
> instance, is unscannable without listening for NDP at the same time -- and
> from a remote network, you can basically forget it.

	And I expect that machines using stateless autoconfig will
	update their forward and reverse records in the DNS.  The
	reasons for doing this are independent of the mechanism of
	address assignment.  Too many services will not work unless
	there is a valid PTR / address combination.
> You're also assuming that there will be PTR records for the most commonly
> infectable OS ([vendor product elided]) in the most commonly used
> configuration (desktop).  It's highly likely that such systems will use some
> sort of autoconfiguration, and stateless form as above presents a fairly
> large address space to scan.  If there are PTRs assigned for such hosts at
> all, the attack vector is actually somewhat simple to minimize:  have the
> DNS product in use return empty NOERROR, rather than NXDOMAIN, for any
> unassigned addresses in the /64.
> Don't get me wrong, I'm not one for security through obscurity in the
> primary case.  But attack vector minimization is still useful for this
> particular angle.
> -- 
> -- Todd Vierling <tv at> <tv at> <todd at>
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark_Andrews at

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