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

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

Description:

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.

Impact:

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

CVSS Vector: CVSS:3.1/AV:N/AC:L/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:L/PR:N/UI:N/S:U/C:N/I:N/A:H&version=3.1.

Workarounds:

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

Active exploits:

We are not aware of any active exploits.

Solution:

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

Acknowledgments:

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 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/pgpkey/. If you are unable to use encrypted email you may also report new issues at: https://www.isc.org/reportbug/.

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/download/.

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 https://kb.isc.org/docs/aa-00861.

The Knowledgebase article https://kb.isc.org/docs/cve-2023-2829 is the complete and official security advisory document.

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