CVE-2020-8623: A flaw in native PKCS#11 code can lead to a remotely triggerable assertion failure in pk11.c
  • 20 Aug 2020
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CVE-2020-8623: A flaw in native PKCS#11 code can lead to a remotely triggerable assertion failure in pk11.c

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Article summary

CVE: CVE-2020-8623

Document version: 2.0

Posting date: 20 August 2020

Program impacted: BIND

Versions affected: BIND 9.10.0 -> 9.11.21, 9.12.0 -> 9.16.5, 9.17.0 -> 9.17.3, also affects 9.10.5-S1 -> 9.11.21-S1 of the BIND 9 Supported Preview Edition

Severity: Medium

Exploitable: Remotely


If BIND is built with "--enable-native-pkcs11" then a specially crafted query for a zone signed with RSA can trigger an assertion failure.


An attacker that can reach a vulnerable system with a specially crafted query packet can trigger a crash.

To be vulnerable, the system must:
* be running BIND that was built with "--enable-native-pkcs11"
* be signing one or more zones with an RSA key
* be able to receive queries from a possible attacker

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 9.11.22
  • BIND 9.16.6
  • BIND 9.17.4

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

  • BIND 9.11.22-S1

Acknowledgments: ISC would like to thank Lyu Chiy 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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