CVE-2017-3143: An error in TSIG authentication can permit unauthorized dynamic updates

An attacker may be able to forge a valid TSIG or signature for a dynamic update.

CVE: CVE-2017-3143

Document version: 2.0

Posting date: 29 June 2017

Program impacted: BIND

Versions affected: 9.4.0->9.8.8, 9.9.0->9.9.10-P1, 9.10.0->9.10.5-P1, 9.11.0->9.11.1-P1, 9.9.3-S1->9.9.10-S2, 9.10.5-S1->9.10.5-S2

Severity: High

Exploitable: Remotely

Description:

An attacker who is able to send and receive messages to an authoritative DNS server, and who has knowledge of a valid TSIG key name for the zone and service being targeted, may be able to manipulate BIND 9 into accepting an unauthorized dynamic update.

Impact:

A server that relies solely on TSIG keys with no other address-based ACL protection could be vulnerable to malicious zone content manipulation using this technique.

Note that the local update policy (configured with "update-policy local;" in named.conf) implicitly defines a key with a known key name (local-ddns) and default algorithm and no IP-based access controls on the zone updates. In conjunction with this failure in TSIG verification, "update-policy local" is potentially very dangerous.

CVSS Score: 7.5

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

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:L/PR:N/UI:N/S:U/C:N/I:H/A:N.

Workarounds:

The effects of this vulnerability can be mitigated by using Access Control Lists (ACLs) that require both address range validation and use of TSIG authentication. For information on how to configure this type of compound authentication control, please see: Using Access Control Lists (ACLs) with both addresses and keys.

Administrators who have used named.conf option "update-policy local;" should patch their servers as soon as possible; if this is not possible, they should replace the update-policy configuration statement with both an allow-update statement implementing the key requirement for updates and also imposing an IP ACL limitation, e.g.:

allow-update { !{ !localhost; }; key local-ddns; };

Active exploits:

No known active exploits, but a similar issue was announced publicly on 23 June 2017 by another DNS server software provider.

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-P2
• BIND 9 version 9.10.5-P2
• BIND 9 version 9.11.1-P2

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

• BIND 9 version 9.9.10-S3
• BIND 9 version 9.10.5-S3

Acknowledgements: ISC would like to thank Clément Berthaux from Synacktiv for reporting this issue.

Document Revision History:

1.0 Advance Notification, 26 June 2017
1.1 CVSS score corrected (was previously erroneously listed as 7.8), 27 June 2017
1.2 Update phrasing in the Workarounds section; Correct date of similar public announcement, 29 June 2017
1.3 Remove references to SIG(0), which is not affected, 29 June 2017
2.0 Public disclosure, 29 June 2017
2.1 "Impact" and "Workarounds" updated to better explain "update-policy local;" risk, 6 July 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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