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Re: bind dos info?
From: Michael Wood <itnetsec () gmail com>
Date: Wed, 16 Nov 2011 21:06:42 -0500

Nope...I haven't seen anything yet either.  Maybe someone else can
enlighten us? ;)
On Nov 16, 2011 9:05 PM, "Larry W. Cashdollar" <bugs () fbi dhs org> wrote:

Thanks Michael!
 I guess 'ISC is working on determining the ultimate cause by which a
record with this particular inconsistency is cached' is the part I'm
interested in reading about and there are no details yet..

http://www.isc.org/software/bind/advisories/cve-2011-4313
On Nov 16, 2011 8:53 PM, "Larry W. Cashdollar" <bugs () fbi dhs org> wrote:

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?

Thanks
-- Larry C$


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_______________________________________________
Full-Disclosure - We believe in it.
Charter: http://lists.grok.org.uk/full-disclosure-charter.html
Hosted and sponsored by Secunia - http://secunia.com/

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