CVE-2023-2829: Malformed NSEC records can cause named to terminate unexpectedly when synth-from-dnssec is enabled
  • 21 Jun 2023
  • 2 Minutes to read
  • Contributors
  • Dark
  • PDF

CVE-2023-2829: Malformed NSEC records can cause named to terminate unexpectedly when synth-from-dnssec is enabled

  • Dark
  • PDF

Article summary

CVE: CVE-2023-2829

Document version: 2.0

Posting date: 21 June 2023

Program impacted: BIND 9

Versions affected:

BIND Supported Preview Edition

  • 9.16.8-S1 -> 9.16.41-S1
  • 9.18.11-S1 -> 9.18.15-S1

Severity: High

Exploitable: Remotely


A named instance configured to run as a DNSSEC-validating recursive resolver with the Aggressive Use of DNSSEC-Validated Cache (RFC 8198) option (synth-from-dnssec) enabled can be remotely terminated using a zone with a malformed NSEC record.


By sending specific queries to the resolver, an attacker can cause named to terminate unexpectedly.

Note that the BIND configuration option synth-from-dnssec is enabled by default in all versions of BIND 9.18 and 9.18-S and newer. In earlier versions of BIND that had this option available, it was disabled unless activated explicitly in named.conf.

CVSS Score: 7.5


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


Setting synth-from-dnssec to no prevents the problem.

Active exploits:

We are not aware of any active exploits.


Upgrade to the patched release most closely related to your current version of BIND 9:

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

  • 9.16.42-S1
  • 9.18.16-S1


ISC would like to thank Greg Kuechle from SaskTel for bringing this vulnerability to our attention.

Document revision history:

  • 1.0 Early Notification, 14 June 2023
  • 2.0 Public disclosure, 21 June 2023

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 be mailed 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 at

The Knowledgebase article 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.