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Re: Interesting paper by Steve Bellovin - Worm propagation in a v6 internet
From: Mark Andrews <Mark_Andrews () isc org>
Date: Wed, 15 Feb 2006 16:00:41 +1100

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 () duh org> <tv () pobox com> <todd () vierling name>
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark_Andrews () isc org

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