Re: bind dos info?

[Jeffrey Walton <noloader () gmail com>]

On Wed, Nov 16, 2011 at 9:13 PM,  <Valdis.Kletnieks () vt 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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