--- title: "CVE-2023-4236" slug: "cve-2023-4236" description: "A flaw in the networking code handling DNS-over-TLS queries may cause named to terminate unexpectedly due to an assertion failure." updated: 2023-09-20T11:49:42Z published: 2023-09-20T11:49:42Z --- > ## 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-2023-4236: named may terminate unexpectedly under high DNS-over-TLS query load **CVE:** [CVE-2023-4236](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-4236) **Document version:** 2.0 **Posting date:** 20 September 2023 **Program impacted:** [BIND 9](https://www.isc.org/bind/) **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](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](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 be mailed to [bind-security@isc.org](mailto:bind-security@isc.org) or posted as confidential GitLab issues at [https://gitlab.isc.org/isc-projects/bind9/-/issues/new?issue[confidential]=true](https://gitlab.isc.org/isc-projects/bind9/-/issues/new?issue%5Bconfidential%5D=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/](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](https://kb.isc.org/docs/aa-00861). The Knowledgebase article [https://kb.isc.org/docs/cve-2023-4236](https://kb.isc.org/docs/cve-2023-4236) 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.