full-disclosure - Re: bind dos info?

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Date: Thu, 17 Nov 2011 21:26:16 -0500
From: Jeffrey Walton <noloader@...il.com>
To: Valdis.Kletnieks@...edu
Cc: full-disclosure@...ts.grok.org.uk
Subject: Re: bind dos info?

On Wed, Nov 16, 2011 at 9:13 PM,  <Valdis.Kletnieks@...edu> wrote:
> 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...)
Am I the only guy wondering why an assert is present in production
code? Was -DNDEBUG accidentally omitted? Or is a crash expected
behavior? I don't believe its the later, since its a DoS with CVE.

Jeff

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