CVE-2015-8461: A race condition when handling socket errors can lead to an assertion failure in resolver.c
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CVE-2015-8461: A race condition when handling socket errors can lead to an assertion failure in resolver.c

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Article summary

CVE: CVE-2015-8461

Document version: 2.0

Posting date: 15 December 2015

Program impacted: BIND

Versions affected: 9.9.8 -> 9.9.8-P1, 9.9.8-S1 -> 9.9.8-S2, 9.10.3 -> 9.10.3-P1

Severity: Medium

Exploitable: Remotely


Beginning with the September 2015 maintenance releases 9.9.8 and 9.10.3, an error was introduced into BIND 9 which can cause a server to exit after encountering an INSIST assertion failure in resolver.c.


An uncommonly occurring condition can cause affected servers to exit with an INSIST failure depending on the outcome of a race condition in resolver.c. While difficult to exploit reliably, a malicious party could, through deliberate behavior, significantly increase the probability of encountering the triggering condition, resulting in denial of service to clients if successful.

CVSS Score: 5.4

CVSS Vector: (AV:N/AC:H/Au:N/C:N/I:N/A:C)

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

Workarounds: None.

Active exploits: None known.

Solution: Upgrade to the patched release most closely related to your current version of BIND. Public open-source branches can be downloaded from

  • BIND 9 version 9.9.8-P2
  • BIND 9 version 9.10.3-P2

BIND 9 Supported Preview edition is a feature preview version of BIND provided exclusively to eligible ISC Support customers.

  • BIND 9 version 9.9.8-S3

Acknowledgements: ISC would like to thank John O'Brien of the University of Pennsylvania for discovering this issue.

Document Revision History:

1.0 Advance Notification. 8 December 2015 2.0 Public Disclosure. 15 December 2015

Related Documents: See our BIND 9 Security Vulnerability Matrix for a complete listing of Security Vulnerabilities and versions affected.

If you'd like more information on ISC Subscription Support and Advance Security Notifications, please visit

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:

Note: 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.

This Knowledgebase article is the complete and official security advisory document.

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