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

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Article summary

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


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.


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


For more information on the Common Vulnerability Scoring System and to obtain your specific environmental score please visit:


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.


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.

Do you still have questions? Questions regarding this advisory should go to To report a new issue, please encrypt your message using's PGP key which can be found here: If you are unable to use encrypted email, you may also report new issues at:


ISC patches only currently supported versions. When possible we indicate EOL versions affected. (For current information on which versions are actively supported, please see

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.

This Knowledgebase article is the complete and official security advisory document.

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