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CVE-2017-3143: An error in TSIG authentication can permit unauthorized dynamic updates
Author: Michael McNally Reference Number: AA-01503 Views: 58303 Created: 2017-06-29 19:30 Last Updated: 2017-07-06 21:07 0 Rating/ Voters

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

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 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 in conjunction.  For information on how to configure this type of compound authentication control, please see: https://kb.isc.org/article/AA-00723/0/Using-Access-Control-Lists-ACLs-with-both-addresses-and-keys.html.

Administrators who have made use of named.conf option "update-policy local;" should patch their servers as soon as possible and if this is not possible should replace the update-policy configuration statement with an allow-update statement implementing the key requirement for updates but additionally 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 BIND9 Security Vulnerability Matrix at https://kb.isc.org/article/AA-00913 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 http://www.isc.org/support/.

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 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 http://www.isc.org/downloads/). 

ISC Security Vulnerability Disclosure Policy:  Details of our current security advisory policy and practice can be found here: https://kb.isc.org/article/AA-00861/164/ISC-Software-Defect-and-Security-Vulnerability-Disclosure-Policy.html

This Knowledge Base article https://kb.isc.org/article/AA-01503 is the complete and official security advisory document.

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