On Tue, Dec 10, 2013 at 2:43 PM, Doug Barton <dougb(_at_)dougbarton(_dot_)us>
wrote:
On 12/10/2013 06:00 AM, John C Klensin wrote:
As previously mentioned, these attacks are theoretically possible, but
they are trivially detectable since all of the critical data is visible in
the DNS. They may not be _immediately_ detectable, and in fact likely would
not be detected immediately; where "immediate" is going to vary widely
depending on the value/profile of the target. But we have plenty of
experience with people noticing DNS problems for critical resources. Even
in the DNSSEC case we have major players doing DNSSEC validation now
(Comcast and Google leap to mind) so shenanigans involving DNSSEC are going
to be noticed.
As we learned with the WebPKI, that is only the case if you have a deployed
monitoring infrastructure. It is not that difficult to do but you do have
to do it.
The point I'm trying to get across here is that any sort of manipulation
of the DNS by a 3rd party (such as a malicious hack, NSL, etc.) is valuable
only to the extent that it can go unnoticed, and therefore cause innocent
end users to depend on the 3rd party's resources instead of the valid ones
_without their knowledge_.
Covert attacks are detectable. But that is only a defense if you have the
ability to switch to another root or override the trust assertions of the
root.
We don't need DNSSEC to see that this sort of thing only works for a
limited time. We have had lots of events where high profile sites have had
their registrar data changed, and there is a huge public hue and cry. Of
course a skillful attacker could create a phishing page that looks enough
like the real site to gather a non-trivial number of user passwords, but
again, we don't need DNSSEC for that. In fact, if the sophisticated
attacker manages to socially engineer the registrar credentials (the most
popular form of this type of attack) then they can update the DS record in
addition to the NS records, and have a fake site that validates perfectly.
But people do need to be careful about DANE and about Certificate pinning.
But even that sort of attack would only work for a short period of time.
More importantly, the ability to slide the malicious data into the DNS at
all is going to be proportional to the location of the resource in the
tree. We already know that individual zones are vulnerable to registrar
attacks. However new TLD DS records in the root are greeted with fanfare
(at least amongst a fairly substantial number of DNS wonks), so the ability
to slip stuff in at that level is minimal at best. This is more true at the
root itself.
So to be concise (yeah, I know, too late) claiming that DNSSEC is
vulnerable to external manipulation at the root or TLD level is almost
certainly wrong. There are theoretical attacks that could be launched, but
their practical value is nil. If someone has a valid attack that uses a
method I haven't taken into account, they should find a trusted channel to
make that known.
If we are comparing like with like, the practical value of the attacks
against the WebPKI have been limited, with the exception of DigiNotar
(2) In a different version of some of the comments on the
thread, the "where to validate" question is important. If one
tries to validate at the endpoints, endpoint systems, including
embedded ones, should have the code and resources needed to
validate certs and handle rollovers, even under hostile
conditions, and that isn't easy. If one relies on intermediate,
especially third-party, servers to validate, than much of the
expected integrity protection is gone... and the number of times
such servers have been compromised would make this a
non-theoretical problem even without concerns about
governmental-type attacks (NSL and otherwise) on those servers.
No easy solutions here.
Again, spot on. I've been saying for many years now that the most
interesting part of DNSSEC is going to be local on the end user side.
Pushing validation all the way down is critical.
But if you do that you eliminate the wiggle room that your earlier argument
relied on.
You can solve any security problem if you have an intelligent party with
global knowledge making the decisions. But you can only deploy code at the
end point that is Turing complete and works on the information visible to
it there.
If we are proposing to only do verification in a resolver then the NSL etc.
issues are manageable because it is a service in the cloud and can be
reconfigured.
But the WebPKI works end to end and has the entire decision process
embedded in the end point code. If you want to use DNSSEC end to end you
have to meet the same requirement. In that scenario your proposal that we
deal with lock in issues by using common sense is now a deus ex machina
because machines don't have common sense.
--
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