new DNS forwarder vulnerability

Jared Mauch jared at puck.nether.net
Wed Apr 2 12:54:47 UTC 2014


On Apr 2, 2014, at 8:38 AM, Mark Allman <mallman at icir.org> wrote:

> 
> [catching up]
> 
>> That's a good question, but I know that during the ongoing survey
>> within the Open Resolver Project [http://openresolverproject.org/],
>> Jared found thousands of CPE devices which responded as resolvers.
> 
> Not thousands, *tens of millions*.
> 
> Our estimate from mid-2013 was 32M such devices (detailed in an IMC
> paper last year; http://www.icir.org/mallman/pubs/SCRA13/).  And, that
> roughly agrees with both the openresolverproject.org numbers and another
> (not public) study I know of.  And, as if that isn't bad enough
> ... there is a 2010 IMC paper that puts the number at 15M.  I.e., the
> instances of brokenness are getting worse---doubling in 3 years!  UGH.

One observation: The OpenResolverProject collects responses that come from
ports that the query was not sent to (ie: device responds from UDP/12345 not
from UDP/53, which obviously is broken and doesn't "work", but they actually
return DNS payload which can be used for abuse).

Some good news though:

http://openresolverproject.org/breakdown-graph1.cgi

Since the start of 2014 there seem to be new CPE devices out there that are resolving this issue.  The linear nature of the line in the decrease doesn't seem to be something like "ISPs" started blocking udp/53 to customers, which would appear more like a step function.

I'm aware of some other studies ongoing to fingerprint CPE and their behaviors/aggregated resolver dependencies.  I expect to see some of that data presented at the upcoming DNS-OARC meeting in Warsaw.

Getting everyone to update their firmware on devices would go a long way as well.  Some vendors have no software QA on this front so add/remove the response on the WAN interface as their releases march forward.

- Jared



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