CVE-2023-6516: Specific recursive query patterns may lead to an out-of-memory condition
  • 13 Feb 2024
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CVE-2023-6516: Specific recursive query patterns may lead to an out-of-memory condition

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Article Summary

CVE: CVE-2023-6516

Title: Specific recursive query patterns may lead to an out-of-memory condition

Document version: 2.0

Posting date: 13 February 2024

Program impacted: BIND 9

Versions affected:


  • 9.16.0 -> 9.16.45

BIND Supported Preview Edition

  • 9.16.8-S1 -> 9.16.45-S1

Severity: High

Exploitable: Remotely


To keep its cache database efficient, named running as a recursive resolver occasionally attempts to clean up the database. It uses several methods, including some that are asynchronous: a small chunk of memory pointing to the cache element that can be cleaned up is first allocated and then queued for later processing. It was discovered that if the resolver is continuously processing query patterns triggering this type of cache-database maintenance, named may not be able to handle the cleanup events in a timely manner. This in turn enables the list of queued cleanup events to grow infinitely large over time, 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 environmental factors, but 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:

  • 9.16.48

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

  • 9.16.48-S1


ISC would like to thank Infoblox for bringing this vulnerability to our attention.

Document revision history:

  • 1.0 Early Notification, 10 January 2024
  • 1.1 Revised Early Notification, 15 January 2024
  • 1.2 Revised the list of fixed versions, 11 February 2024
  • 2.0 Public disclosure, 13 February 2024

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 or posted as confidential GitLab issues at[confidential]=true.


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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