full-disclosure - Re: bind dos info?

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Date: Wed, 16 Nov 2011 21:13:45 -0500
From: Valdis.Kletnieks@...edu
To: "Larry W. Cashdollar" <bugs@....dhs.org>
Cc: full-disclosure@...ts.grok.org.uk
Subject: Re: bind dos info?

On Thu, 17 Nov 2011 11:51:09 EST, "Larry W. Cashdollar" said:
> Hello list,
> I am wondering if anyone has more details on the bind9 DoS that just came
> out? (CVE-2011-4313) from what I can tell it appears a negative cached DNS
> object with a valid RR response associated with it(which shouldn't exist)
> will cause a vulnerabile bind9 server to crash.
> 
> See lines 1890 - 1896 of query.c
> 1890         if (result == DNS_R_NCACHENXRRSET) {
> 1891                 dns_rdataset_disassociate(rdataset);
> 1892                 /*
> 1893                  * Negative cache entries don't have sigrdatasets.
> 1894                  */
> 1895                 INSIST(! dns_rdataset_isassociated(sigrdataset));
> 1896         }
> 
> 
> Since allowing recursive queries must be enabled for this to work the
> attacker  must force a vulnerable dns server to query a malicous DNS
> server by asking it to look up an NXrecord for a domain the attacker
> controls dns for.  Sending a response of NXdomain but having actual DNS
> results in the response.
> 
> I am wondering if someone has seen a good write up out there?

See above. :)  (Seriously, that's a good one-para summary analysis of the
issue, better than a lot of 3rd-party advisories we see...)

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