CVE-2023-4236: named may terminate unexpectedly under high DNS-over-TLS query load

CVE: CVE-2023-4236

Document version: 2.0

Posting date: 20 September 2023

Program impacted: BIND 9

Versions affected:

BIND

• 9.18.0 -> 9.18.18

BIND Supported Preview Edition

• 9.18.11-S1 -> 9.18.18-S1

Severity: High

Exploitable: Remotely

Description:

A flaw in the networking code handling DNS-over-TLS queries may cause named to terminate unexpectedly due to an assertion failure. This happens when internal data structures are incorrectly reused under significant DNS-over-TLS query load.

Impact:

A named instance vulnerable to this flaw may terminate unexpectedly when subjected to significant DNS-over-TLS query load.

This flaw does not affect DNS-over-HTTPS code, as that uses a different TLS implementation.

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:

Disabling listening for DNS-over-TLS connections (by removing listen-on ... tls ... { ... }; statements from the configuration) prevents the affected code paths from being taken, rendering exploitation impossible. However, there is no workaround for this flaw if DNS-over-TLS support is required.

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:

• 9.18.19

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

• 9.18.19-S1

Acknowledgments:

ISC would like to thank Robert Story from the USC/ISI DNS root server operations team for bringing this vulnerability to our attention.

Document revision history:

• 1.0 Early Notification, 13 September 2023
• 2.0 Public disclosure, 20 September 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 bind-security@isc.org or posted as confidential GitLab issues at https://gitlab.isc.org/isc-projects/bind9/-/issues/new?issue[confidential]=true.

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-2023-4236 is the complete and official security advisory document.

Legal Disclaimer:

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