Re: [Resolverless-dns] Paper on Resolver-less DNS

Erik Sy <sy@informatik.uni-hamburg.de> Mon, 02 September 2019 20:52 UTC

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From: Erik Sy <sy@informatik.uni-hamburg.de>
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Date: Mon, 2 Sep 2019 22:52:30 +0200
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Subject: Re: [Resolverless-dns] Paper on Resolver-less DNS
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On 8/30/19 07:30, Viktor Dukhovni wrote:
> On Thu, Aug 29, 2019 at 11:28:13PM +0200, Erik Sy wrote:
>
>> On 8/29/19 17:34, Viktor Dukhovni wrote:
>>> Resolver-less DNS as proposed disregards long-standing defenses
>>> against address forgery by third parties,
>> Can you please explain this point?
> IIRC the protocol allows any authenticated server (with Let's
> Encrypt, that's everybody) to return "out-of-bailiwick" answers
> (for any unrelated domain).
>
> Yes, a client's designated resolver can also do that, but some
> clients perform local DNSSEC validation,
Can you name a popular client doing DNSSEC validation in a web browsing
scenario?
>  and in any case there's a
> big difference between trusting name resolution to a set of dedicated
> resolvers, vs. each and every server one happens to visit (by
> clicking on a malicious link for example).
Note, that in resolver-less DNS the client does not trust received DNS
records like it is common for the traditional DNS. Instead, the client
validates these DNS records.
>
>>>  breaks geo load-balancing,
>> No, there are no new issues with geo load-balancing compared to using a
>> public DNS resolver.
> Well, the public DNS resolvers (which I do not use on my network)
> typically pass an EDNS0 client-subnet option to the upstream
> authoritative server.  I don't recall anything similar in the paper.
It is in the paper (see Section 4.3).
>
> But if we're doing away with geo load-balancing, and moving to only
> using anycast IPs to reduce latency, that's fine by me, there are
> other more important problems.
>
>>> It introduce a new cache-poisoning channel, and surprising differences
>>> between the IP addresses a browser might use to reach a site from cold
>>> start vs. after visiting some unrelated site.
>> Also traditional DNS resolvers are vulnerable to cache-poisoning attacks.
> Not with DNSSEC validation,
Do you mean the client is doing DNSSEC validation?
>  and modestly difficult off-path.  But
> with this proposal, you get cache poisoing by design from any
> off-path server the client happens to visit.

Do you mind describing an concrete attack?

>
>>> In the case of IPv6 it can be used to fingerprint and track clients by
>>> giving them ephemeral client-specific addresses (in the server's /64
>>> or broader prefix) for third-party servers, and then proxying their
>>> connections (at layer 4) to the real server, while tracking the
>>> client's access to each site.
>> This tracking mechanism is also feasible using traditional DNS.
> But not available to every off-path server I visit.
It is an easy task for an web server to track user visits to other sites
by using for example redirects as Google Search is doing.
>   My resolver
> does not do that. 
First, it is quite uncommon that people run their own DNS resolver.
Second, running an own DNS resolver generates new privacy and
performance problems.
>  Your proposal would delegate this ability
> to every random server I visit.  That's a security fail.

I do not understand why this should be a security fail. In my opinion it
is not even an additional privacy failure because the privacy leak
existed before using common techniques such as redirects. 

Erik