CVE-2023-5517: Querying RFC 1918 reverse zones may cause an assertion failure when nxdomain-redirect is enabled
  • 13 Feb 2024
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CVE-2023-5517: Querying RFC 1918 reverse zones may cause an assertion failure when nxdomain-redirect is enabled

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Article summary

CVE: CVE-2023-5517

Title: Querying RFC 1918 reverse zones may cause an assertion failure when "nxdomain-redirect" is enabled

Document version: 2.0

Posting date: 13 February 2024

Program impacted: BIND 9

Versions affected:


  • 9.12.0 -> 9.16.45
  • 9.18.0 -> 9.18.21
  • 9.19.0 -> 9.19.19

BIND Supported Preview Edition

  • 9.16.8-S1 -> 9.16.45-S1
  • 9.18.11-S1 -> 9.18.21-S1

Severity: High

Exploitable: Remotely


A flaw in query-handling code can cause named to exit prematurely with an assertion failure when:

  • nxdomain-redirect <domain>; is configured, and
  • the resolver receives a PTR query for an RFC 1918 address that would normally result in an authoritative NXDOMAIN response.


If both of the above conditions are met, a single suitable query will cause named to crash.

CVSS Score: 7.5


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


Disabling the nxdomain-redirect feature makes the faulty code path impossible to reach, preventing this flaw from being exploitable.

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:

  • 9.16.48
  • 9.18.24
  • 9.19.21

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

  • 9.16.48-S1
  • 9.18.24-S1

Document revision history:

  • 1.0 Early Notification, 10 January 2024
  • 1.1 Revised Early Notification, 15 January 2024
  • 1.2 Revised the list of fixed versions, 11 February 2024
  • 2.0 Public disclosure, 13 February 2024

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 or posted as confidential GitLab issues at[confidential]=true.


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.

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