Software Engineering Institute

According to ISC:

An as-yet unidentified network event caused BIND 9 resolvers to cache an invalid record, subsequent queries for which could crash the resolvers with an assertion failure. ISC is working on determining the ultimate cause by which a record with this particular inconsistency is cached.At this time we are making available a patch which makes named recover gracefully from the inconsistency, preventing the abnormal exit.

The patch has two components. When a client query is handled, the code which processes the response to the client has to ask the cache for the records for the name that is being queried. The first component of the patch prevents the cache from returning the inconsistent data. The second component prevents named from crashing if it detects that it has been given an inconsistent answer of this nature.

A remote, unauthenticated attacker can cause the BIND 9 resolver to crash creating a denial of service condition.

Apply an update

Users who obtain BIND from a third-party vendor, such as their operating system vendor, should see the vendor information portion of this document for a partial list of affected vendors.

This vulnerability is addressed in ISC BIND versions 9.4-ESV-R5-P1, 9.6-ESV-R5-P1, 9.7.4-P1 and 9.8.1-P1. Users of BIND from the original source distribution should upgrade to this version.

See also http://www.isc.org/software/bind/advisories/cve-2011-4313