CVE-2022-3924: named configured to answer from stale cache may terminate unexpectedly at recursive-clients soft quota
  • 25 Jan 2023
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CVE-2022-3924: named configured to answer from stale cache may terminate unexpectedly at recursive-clients soft quota

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Article summary

CVE: CVE-2022-3924

Document version: 2.0

Posting date: 25 January 2023

Program impacted: BIND 9

Versions affected:


  • 9.16.12 -> 9.16.36
  • 9.18.0 -> 9.18.10
  • 9.19.0 -> 9.19.8

BIND Supported Preview Edition

  • 9.16.12-S1 -> 9.16.36-S1

(The flaw exists in the implementation of the stale-answer-client-timeout option, which was first effectively introduced in BIND 9.16.12 and BIND 9.16.12-S1. That option is also configurable in BIND 9.11.33-S1 and newer BIND 9.11-S versions, but it is always replaced with 0 in all BIND 9.11.x-S1 releases.)

Severity: High

Exploitable: Remotely


This issue can affect BIND 9 resolvers with stale-answer-enable yes; that also make use of the option stale-answer-client-timeout, configured with a value greater than zero.

If the resolver receives many queries that require recursion, there will be a corresponding increase in the number of clients that are waiting for recursion to complete. If there are sufficient clients already waiting when a new client query is received so that it is necessary to SERVFAIL the longest waiting client (see BIND 9 ARM recursive-clients limit and soft quota), then it is possible for a race to occur between providing a stale answer to this older client and sending an early timeout SERVFAIL, which may cause an assertion failure.


By sending specific queries to the resolver, an attacker can cause named to crash.

CVSS Score: 7.5


For more information on the Common Vulnerability Scoring System and to obtain your specific environmental score please visit:


Disabling stale-answer-client-timeout entirely or setting the timeout value to zero prevents the problem.

It is not possible to disable the limit on recursive-clients, though it could be set to a very high value in order to reduce the likelihood of encountering this scenario. However, this is not recommended as the limit on recursive clients is important for preventing exhaustion of server resources.

Active exploits:

We are not aware of any active exploits.


Upgrade to the patched release most closely related to your current version of BIND 9:

  • 9.16.37
  • 9.18.11
  • 9.19.9

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

  • 9.16.37-S1


ISC would like to thank Maksym Odinintsev from AWS for bringing this vulnerability to our attention.

Document revision history:

  • 1.0 Early Notification, 18 January 2023
  • 2.0 Public disclosure, 25 January 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 To report a new issue, please encrypt your message using's PGP key, which can be found here: If you are unable to use encrypted email you may also report new issues at:


ISC patches only currently supported versions. When possible we indicate EOL versions affected. For current information on which versions are actively supported, please see

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

The Knowledgebase article is the complete and official security advisory document.

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