CVE-2016-2088: A response containing multiple DNS cookies causes servers with cookie support enabled to exit with an assertion failure.

[Michael McNally]

CVE:                   CVE-2016-2088
Document Version:      2.0
Posting date:          09 March 2016
Program Impacted:      BIND
Versions affected:     9.10.0 -> 9.10.3-P3
Severity:              High
Exploitable:           Remotely

Description:

   BIND 9.10 has preliminary support for DNS cookies (or source
   identity tokens), a proposed mechanism designed to allow lightweight
   transaction security between a querying party and a nameserver.
   An error in the BIND code implementing support for this optional
   feature permits a deliberately misconstructed packet containing
   multiple cookie options to cause named to terminate with an
   INSIST assertion failure in resolver.c if DNS cookie support is
   enabled in the server.  Only servers with DNS cookie support
   enabled at build time can be affected by this defect; in servers
   which do not have DNS cookie support selected any cookies
   encountered will be ignored as unknown option types.

Impact:

   Servers which are built with DNS cookie support enabled are
   vulnerable to denial of service if an attacker can cause them
   to receive and process a response that contains multiple cookie
   options.

CVSS Score:            7.8
CVSS Vector:           (AV:N/AC:L/Au:N/C:N/I:N/A:C)

For more information on the Common Vulnerability Scoring System and
to obtain your specific environmental score please visit:
https://nvd.nist.gov/cvss.cfm?calculator&version=2&vector=(AV:N/AC:L/Au:N/C:N/I:N/A:C)

Workarounds:

   Servers which do not have cookie support included are not at
   risk from this vulnerability.

   When BIND 9.10 is built from ISC-supported source, cookie support
   is not selected by default.  In order to be included it must be
   elected using the "--enable-sit" command-line argument when
   running the "configure" script in the top level source directory.
   Operators with affected servers can re-configure and re-build
   BIND without cookie support if they prefer not to upgrade to a
   release containing the fix. However, ISC-provided binary packages
   for Windows do have "--enable-sit" selected.  Server operators
   using the Windows binary packages should upgrade to the corrected
   version.

Active exploits:

   No known active exploits.

Solution: 

   Re-configure and re-build BIND without enabling cookie support
   or upgrade to the patched release most closely related to your
   current version of BIND.

   - BIND 9 version 9.10.3-P4

Document Revision History:

   1.0 Advance Notification 02 March 2016
   2.0 Public Disclosure.  09 March 2016

Related Documents:

   See our BIND9 Security Vulnerability Matrix at
   https://kb.isc.org/article/AA-00913 for a complete listing of
   Security Vulnerabilities and versions affected.

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