---
title: "CVE-2019-6476: An error in QNAME minimization code can cause BIND to e"
slug: "cve-2019-6476"
description: "CVE-2019-6476: An error in QNAME minimization code can cause BIND to exit with an assertion failure"
updated: 2019-10-16T17:38:29Z
published: 2019-10-16T17:38:30Z
---

> ## Documentation Index
> Fetch the complete documentation index at: https://kb.isc.org/llms.txt
> Use this file to discover all available pages before exploring further.

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

**CVE:** [CVE-2019-6476](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-6476)

**Document version:** 2.0

**Posting date:** 16 October 2019

**Program impacted:** [BIND](https://www.isc.org/downloads/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](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&version=3.1).

**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](https://kb.isc.org/docs/aa-00913) for a complete listing of security vulnerabilities and versions affected.

**Do you still have questions?** Questions regarding this advisory should go to [security-officer@isc.org](mailto:security-officer@isc.org). *To report a new issue, please encrypt your message using security-officer@isc.org's PGP key which can be found here: [https://www.isc.org/downloads/software-support-policy/openpgp-key/](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/](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/](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](https://kb.isc.org/docs/aa-00861).

This [Knowledgebase article](https://kb.isc.org/docs/cve-2019-6476) is the complete and official security advisory document.

**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.