CVE-2023-4408: Parsing large DNS messages may cause excessive CPU load
  • 13 Feb 2024
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CVE-2023-4408: Parsing large DNS messages may cause excessive CPU load

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Article summary

CVE: CVE-2023-4408

Title: Parsing large DNS messages may cause excessive CPU load

Document version: 2.0

Posting date: 13 February 2024

Program impacted: BIND 9

Versions affected:


  • 9.0.0 -> 9.16.45
  • 9.18.0 -> 9.18.21
  • 9.19.0 -> 9.19.19

(Versions prior to 9.11.37 were not assessed.)

BIND Supported Preview Edition

  • 9.9.3-S1 -> 9.11.37-S1
  • 9.16.8-S1 -> 9.16.45-S1
  • 9.18.11-S1 -> 9.18.21-S1

(Versions prior to 9.11.37-S1 were not assessed.)

Severity: High

Exploitable: Remotely


The DNS message parsing code in named includes a section whose computational complexity is overly high. It does not cause problems for typical DNS traffic, but crafted queries and responses may cause excessive CPU load on the affected named instance by exploiting this flaw. This issue affects both authoritative servers and recursive resolvers.


By flooding the target server with queries exploiting this flaw an attacker can significantly impair the server's performance, effectively denying legitimate clients access to the DNS resolution service.

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
  • 9.18.24
  • 9.19.21

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

  • 9.16.48-S1
  • 9.18.24-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, 10 January 2024
  • 1.1 Early fix withdrawn due to regression, 11 January 2024
  • 1.2 Revised Early Notification, 15 January 2024
  • 1.3 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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