CVE-2019-6471: A race condition when discarding malformed packets can cause BIND to exit with an assertion failure

[Michael McNally]

CVE:                 CVE-2019-6471
Document version:    2.0
Posting date:        19 June 2019
Program impacted:    BIND
Versions affected:   BIND 9.11.0 -> 9.11.7, 9.12.0 -> 9.12.4-P1,
                     9.14.0 -> 9.14.2. Also all releases of the BIND 9.13
                     development branch and version 9.15.0 of the BIND 9.15
                     development branch. BIND Supported Preview Edition
                     versions 9.11.3-S1 -> 9.11.7-S1.
Severity:            Medium
Exploitable:         Remotely

Description:

   A race condition which may occur when discarding malformed packets
   can result in BIND exiting due to a REQUIRE assertion failure
   in dispatch.c.

Impact:

   An attacker who can cause a resolver to perform queries which
   will be answered by a server which responds with deliberately
   malformed answers can cause named to exit, denying service to
   clients.

CVSS Score:          5.9
CVSS Vector:         CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

For more information on the Common Vulnerability Scoring System and
to obtain your specific environmental score please visit:
https://www.first.org/cvss/calculator/3.0#CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H.

Workarounds:

   None.

Active exploits:

   None known.

Solution:

   Upgrade to the patched release most closely related to your current
version of BIND:

   +  BIND 9.11.8
   +  BIND 9.12.4-P2
   +  BIND 9.14.3
   +  BIND 9.15.1

   BIND Supported Preview Edition is a special feature preview
   branch of BIND provided to eligible ISC support customers.

   +  BIND 9.11.8-S1

Acknowledgements:

   ISC would like to thank CERN for helping us to discover this issue.

Document revision history:

   1.0 Early Notification, 12 June 2019
   2.0 Public Disclosure, 19 June 2019

Related documents:

   See our BIND 9 Security Vulnerability Matrix for a complete
   listing of security vulnerabilities and versions affected.

Do you still have questions? Questions regarding this advisory
should go to security-officer at isc.org. To report a new issue, please
encrypt your message using security-officer at isc.org's PGP key which
can be found here:
   https://www.isc.org/downloads/software-support-policy/openpgp-key/
If you are unable to use encrypted email, you may also report new
issues at: https://www.isc.org/community/report-bug/.

Note:

   ISC patches only currently supported versions. When possible we
   indicate EOL versions affected. (For current information on which
   versions are actively supported, please see
   https://www.isc.org/downloads/.)

ISC Security Vulnerability Disclosure Policy:

   Details of our current security advisory policy and practice can
   be found in the ISC Software Defect and Security Vulnerability
   Disclosure Policy.

Legal Disclaimer:

   Internet Systems Consortium (ISC) is providing this notice on
   an "AS IS" basis. No warranty or guarantee of any kind is expressed
   in this notice and none should be implied. ISC expressly excludes
   and disclaims any warranties regarding this notice or materials
   referred to in this notice, including, without limitation, any
   implied warranty of merchantability, fitness for a particular
   purpose, absence of hidden defects, or of non-infringement. Your
   use or reliance on this notice or materials referred to in this
   notice is at your own risk. ISC may change this notice at any
   time. A stand-alone copy or paraphrase of the text of this
   document that omits the document URL is an uncontrolled copy.
   Uncontrolled copies may lack important information, be out of
   date, or contain factual errors.