CVE-2023-2911: Exceeding the recursive-clients quota may cause named to terminate unexpectedly when stale-answer-client-timeout is set to 0
Document version: 2.0
Posting date: 21 June 2023
Program impacted: BIND 9
- 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.)
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.
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.
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
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.
This flaw was discovered in internal testing. We are not aware of any active exploits.
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.
Document revision history:
- 1.0 Early Notification, 14 June 2023
- 2.0 Public disclosure, 21 June 2023
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 [email protected]. To report a new issue, please encrypt your message using [email protected]'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/.
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-2023-2911 is the complete and official security advisory document.
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