CVE-2019-6476: An error in QNAME minimization code can cause BIND to exit with an assertion failure

[Cathy Almond]

CVE:                 CVE-2019-6476
Document version:    2.0
Posting date:        16 October 2019
Program impacted:    BIND
Versions affected:   BIND 9.14.0 -> 9.14.6. Also releases 9.15.0 ->
                     9.15.4 of the BIND 9.15 development branch.
Severity: Medium

Exploitable: Remotely

Description:

   A defect in code added to support QNAME minimization can cause
   named to exit with an assertion failure if a forwarder returns
   a referral rather than resolving the query.

Impact:

   An attacker who manages to deliberately trigger this condition
   on a server which is performing recursion can cause named to
   exit, denying service to clients.

CVSS Score: 5.9

CVSS Vector: CVSS:3.1/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://nvd.nist.gov/vuln-metrics/cvss/v3-calculator?vector=AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H.

Workarounds:

   Servers which have QNAME minimization turned on are potentially
   vulnerable to this defect if they are running an affected version
   of BIND. The vulnerability can be avoided by disabling QNAME
   minimization using "qname-minimization disabled;" in the global
   options section of named.conf (Note: the default value for the
   qname-minimization setting in the 9.14 and 9.15 branches is
   "relaxed". To make use of this workaround it must be explicitly
   disabled.)

Active exploits:

None known.

Solution:

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

   +  BIND 9.14.7
   +  BIND 9.15.5

Document revision history:

   1.0 Early Notification, 09 October 2019
   2.0 Public Disclosure, 16 October 2019

Related documents:

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

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Note:

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   indicate EOL versions affected. (For current information on which
   versions are actively supported, please see
   https://www.isc.org/downloads/.)

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