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full-disclosure-uk: Re: [Full-disclosure] DNS Cache Dan Kamikaze

Re: [Full-disclosure] DNS Cache Dan Kamikaze (Actual Exploit Discussion)

From: Paul Schmehl <pschmehl_lists_at_nospam>
Date: Sun Jul 13 2008 - 20:37:25 GMT
To: eugaaa@gmail.com, full-disclosure@lists.grok.org.uk

--On July 13, 2008 2:50:26 PM -0500 eugaaa@gmail.com wrote:

> http://blogs.zdnet.com/security/?p=1466
> Can someone clarify what they meant by "non-reversible patch" ?

The patch changes the default behavior of dns so that queries are responded to from random ports rather than always from the same port (usually 53.) Reversing the patch merely returns you to the previous default behavior. It does not get you to the vulnerability that, in conjunction with non-random port responses, would allow you to spoof dns queries. (This is speculation on my part. Dan hasn't shared the details me with.) IOW, there is a separate vulnerability in dns, which Dan has not yet revealed, that allows you to take advantage of the non-random nature of query responses.

Readers should note that if you override the patch behavior by specifying a query response port (the syntax is available to do that), you negate the patch.

> http://www.debian.org/security/2008/dsa-1603
> Are these .deb patches automagical?

If you mean, is bind patched after you've followed the directions in the advisory (i.e. run apt-get update and then apt-get install bind9), then yes, it "automagical" as you put it.

> *scratches head*
> I'm not interested in discussing the hype or scene-war aspect of this
> vulnerability.
> Has anyone actually verified the impact of this vulnerability? Any code,
> anything?
> (http://www.milw0rm.com/exploits/4266)

No because the real vulnerability has not yet been released. (Again, this is my speculation.) The patches will make bind much more resistant to a spoofing attack that would have been easy to do once the real vulnerability is revealed publicly.

BTW, if you want to check your name server (so long as it's not doing forwarding), you can run this command:
# dig @yourserver +short porttest.dns-oarc.net TXT

A patched server will respond like this: # dig @ns1.stovebolt.com +short porttest.dns-oarc.net TXT z.y.x.w.v.u.t.s.r.q.p.o.n.m.l.k.j.i.h.g.f.e.d.c.b.a.pt.dns-oarc.net. " is GOOD: 26 queries in 1.3 seconds from 26 ports with std dev 18347.40"

An unpatched server will return POOR: 26 queries in 1.3.seconds from 1 port.

Paul Schmehl
If it isn't already obvious,
my opinions are my own and not
those of my employer.

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