CVE-2023-2828: named's configured cache size limit can be significantly exceeded
  • 21 Jun 2023
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CVE-2023-2828: named's configured cache size limit can be significantly exceeded

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Article summary

CVE: CVE-2023-2828

Document version: 2.0

Posting date: 21 June 2023

Program impacted: BIND 9

Versions affected:


  • 9.11.0 -> 9.16.41
  • 9.18.0 -> 9.18.15
  • 9.19.0 -> 9.19.13

BIND Supported Preview Edition

  • 9.11.3-S1 -> 9.16.41-S1
  • 9.18.11-S1 -> 9.18.15-S1

(Versions prior to 9.11.37 & 9.11.37-S1 were not assessed, but we believe that all versions of BIND 9.11 are vulnerable. Some even older major branches may be vulnerable as well.)

Severity: High

Exploitable: Remotely


Every named instance configured to run as a recursive resolver maintains a cache database holding the responses to the queries it has recently sent to authoritative servers. The size limit for that cache database can be configured using the max-cache-size statement in the configuration file; it defaults to 90% of the total amount of memory available on the host. When the size of the cache reaches 7/8 of the configured limit, a cache-cleaning algorithm starts to remove expired and/or least-recently used RRsets from the cache, to keep memory use below the configured limit.

It has been discovered that the effectiveness of the cache-cleaning algorithm used in named can be severely diminished by querying the resolver for specific RRsets in a certain order, effectively allowing the configured max-cache-size limit to be significantly exceeded.


By exploiting this flaw, an attacker can cause the amount of memory used by a named resolver to go well beyond the configured max-cache-size limit. The effectiveness of the attack depends on a number of factors (e.g. query load, query patterns), but since the default value of the max-cache-size statement is 90%, in the worst case the attacker can exhaust all available memory on the host running named, leading to a denial-of-service condition.

CVSS Score: 7.5


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


No workarounds known.

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:

  • 9.16.42
  • 9.18.16
  • 9.19.14

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


ISC would like to thank Shoham Danino from Reichman University, Anat Bremler-Barr from Tel-Aviv University, Yehuda Afek from Tel-Aviv University, and Yuval Shavitt from Tel-Aviv University for bringing this vulnerability to our attention.

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 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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