CVE-2017-3140: An error processing RPZ rules can cause named to loop endlessly after handling a query

CVE: CVE-2017-3140

Document version: 2.0

Posting date: 14 June 2017

Program impacted: BIND

Versions affected: 9.9.10, 9.10.5, 9.11.0->9.11.1, 9.9.10-S1, 9.10.5-S1

Severity: Medium

Exploitable: Remotely

Description:

If named is configured to use Response Policy Zones (RPZ), an error processing some rule types can lead to a condition where BIND will endlessly loop while handling a query.

Impact:

A server is potentially vulnerable to degradation of service if:

1. the server is configured to use RPZ,
2. the server uses NSDNAME or NSIP policy rules, and
3. an attacker can cause the server to process a specific query.

Successful exploitation of this condition will cause named to enter a state where it continues to loop while processing the query without ever reaching an end state. While in this state, named repeatedly queries the same sets of authoritative nameservers, and this behavior will usually persist indefinitely beyond the normal client query processing timeout. By triggering this condition multiple times, an attacker could cause a deliberate and substantial degradation in service.

Operators of servers that meet the above conditions 1 and 2 may also accidentally encounter this defect during normal operation. It is for this reason that the decision was made to issue this advisory despite its low CVSS score.

CVSS Score: 3.7

CVSS Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

For more information on the Common Vulnerability Scoring System and to obtain your specific environmental score please visit: https://www.first.org/cvss/calculator/3.0#CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L.

Workarounds:

Only the NSDNAME and NSIP RPZ rule types can cause this condition to occur. Administrators can work around this vulnerability if they are able to express their desired policy while avoiding NSDNAME or NSIP rules; otherwise, it is advised that administrators upgrade to a version which corrects the defect.

Active exploits:

No known active exploits, but ISC has received reports of servers accidentally encountering this defect during operation.

Solution: Upgrade to the patched release most closely related to your current version of BIND.  These can all be downloaded from http://www.isc.org/downloads.

• BIND 9 version 9.9.10-P1
• BIND 9 version 9.10.5-P1
• BIND 9 version 9.11.1-P1

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

• BIND 9 version 9.9.10-S2
• BIND 9 version 9.10.5-S2

Acknowledgements: ISC would like to thank Oli Schacher of Switch for bringing this defect to our attention.

Document Revision History:

1.0 Advance Notification, 06 June 2017 2.0 Public Announcement, 14 June 2017

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 security-officer@isc.org. To report a new issue, please encrypt your message using security-officer@isc.org's PGP key which can be found here: https://www.isc.org/downloads/software-support-policy/openpgp-key/. If you are unable to use encrypted email, you may also report new issues at: https://www.isc.org/community/report-bug/.

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 https://www.isc.org/downloads/). 

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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