--- title: "CVE-2023-2911" slug: "cve-2023-2911" description: "CVE-2023-2911: If the recursive-clients quota is reached on a BIND 9 resolver configured with both stale-answer-enable yes; and stale-answer-client-timeout 0;, a sequence of serve-stale-related lookups could cause named to loop and terminate unexpectedly due to a stack overflow." updated: 2023-06-21T13:52:27Z published: 2023-06-21T13:52:27Z --- > ## 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-2023-2911: Exceeding the recursive-clients quota may cause named to terminate unexpectedly when stale-answer-client-timeout is set to 0 **CVE:** [CVE-2023-2911](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-2911) **Document version:** 2.0 **Posting date:** 21 June 2023 **Program impacted:** [BIND 9](https://www.isc.org/bind/) **Versions affected:** BIND * 9.16.33 -> 9.16.41 * 9.18.7 -> 9.18.15 BIND Supported Preview Edition * 9.16.33-S1 -> 9.16.41-S1 * 9.18.11-S1 -> 9.18.15-S1 (BIND 9.11-S versions that support the `stale-answer-client-timeout` option are not vulnerable.) **Severity:** High **Exploitable:** Remotely **Description:** If the `recursive-clients` quota is reached on a BIND 9 resolver configured with both `stale-answer-enable yes;` and `stale-answer-client-timeout 0;`, a sequence of serve-stale-related lookups could cause `named` to loop and terminate unexpectedly due to a stack overflow. **Impact:** By sending specific queries to the resolver, an attacker can cause `named` to terminate unexpectedly. **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:** Setting `stale-answer-client-timeout` to `off` or to a non-zero value prevents the issue. Users of versions 9.18.10, 9.16.36, 9.16.36-S1 or older who are unable to upgrade should set `stale-answer-client-timeout` to `off`; using a non-zero value with these older versions leaves `named` vulnerable to CVE-2022-3924. Although it is possible to set the `recursive-clients` limit to a high number to reduce the likelihood of this scenario, this is not recommended; the limit on `recursive-clients` is important for preventing exhaustion of server resources. The limit cannot be disabled entirely. **Active exploits:** This flaw was discovered in internal testing. We are not aware of any active exploits. **Solution:** Upgrade to the patched release most closely related to your current version of BIND 9: * 9.16.42 * 9.18.16 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 **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](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 [security-officer@isc.org](mailto: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/](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/](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/](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-2023-2911](https://kb.isc.org/docs/cve-2023-2911) is the complete and official security advisory document. **Legal Disclaimer:** Internet Systems Consortium (ISC) is providing this notice on an "AS IS" basis. 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