CVE-2016-9444: An unusually formed DS record response could cause an assertion failure
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CVE-2016-9444: An unusually formed DS record response could cause an assertion failure

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Article summary

CVE: CVE-2016-9444

Document version: 2.0

Posting date: 11 Jan 2017

Program impacted: BIND

Versions affected: 9.6-ESV-R9 -> 9.6-ESV-R11-W1, 9.8.5 -> 9.8.8, 9.9.3 -> 9.9.9-P4, 9.9.9-S1 -> 9.9.9-S6, 9.10.0 -> 9.10.4-P4, 9.11.0 -> 9.11.0-P1

Severity: High

Exploitable: Remotely


An unusually formed answer containing a DS resource record could trigger an assertion failure. While the combination of properties which triggers the assertion should not occur in normal traffic, it is potentially possible for the assertion to be triggered deliberately by an attacker sending a specially constructed answer having the required properties.


This vulnerability occurs during the processing of an answer packet received in response to a query. As a result, recursive servers are at the greatest risk; authoritative servers are at risk only to the extent that they perform a limited set of queries (for example, in order to do zone service - see Why does my authoritative-only nameserver try to query the root nameservers?).

Successful exploitation of this vulnerability will cause named to encounter an assertion failure and stop executing, resulting in denial of service to clients.

CVSS Score: 7.5


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

Workarounds: None known.

Active exploits: No known active exploits.

Solution: Upgrade to the patched release most closely related to your current version of BIND. These can all be downloaded from

  • BIND 9 version 9.9.9-P5
  • BIND 9 version 9.10.4-P5
  • BIND 9 version 9.11.0-P2

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

  • BIND 9 version 9.9.9-S7

Document Revision History:

1.0 Advance Notification, 03 January 2017 2.0 Public Announcement, 11 January 2017

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 security-officer@isc.orgTo 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.

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

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