CVE-2020-8620: A specially crafted large TCP payload can trigger an assertion failure in tcpdns.c
  • 20 Aug 2020
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CVE-2020-8620: A specially crafted large TCP payload can trigger an assertion failure in tcpdns.c

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Article summary

CVE: CVE-2020-8620

Document version: 2.0

Posting date: 20 August 2020

Program impacted: BIND

Versions affected: BIND 9.15.6 -> 9.16.5, 9.17.0 -> 9.17.3

Severity: Medium

Exploitable: Remotely


In versions of BIND that use the libuv network manager (9.16.x is the only stable branch affected) an incorrectly specified maximum buffer size allows a specially crafted large TCP payload to trigger an assertion failure when it is received.


An attacker who can establish a TCP connection with the server and send data on that connection can exploit this to trigger the assertion failure, causing the server to exit.

CVSS Score: 6.7


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:

  • BIND 9.16.6
  • BIND 9.17.4

Acknowledgments: ISC would like to thank Emanuel Almeida of Cisco Systems, Inc. for bringing this vulnerability to our attention.

Document revision history:

1.0 Early Notification, 12 August 2020
1.1 Updated Posting Date, 17 August 2020
2.0 Public Announcement, 20 August 2020

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 go 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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