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CVE-2017-3142: An error in TSIG authentication can permit unauthorized zone transfers
Author: Michael McNally Reference Number: AA-01504 Views: 57762 Created: 2017-06-29 19:30 Last Updated: 2017-06-29 20:31 0 Rating/ Voters

An attacker may be able to circumvent TSIG authentication of AXFR and NOTIFY requests.

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:
Medium
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 may be able to circumvent TSIG authentication of AXFR requests via a carefully constructed request packet.  A server that relies solely on TSIG keys for protection with no other ACL protection could be manipulated into:

  • providing an AXFR of a zone to an unauthorized recipient
  • accepting bogus NOTIFY packets

Impact:

  • An unauthorized AXFR (full zone transfer) permits an attacker to view the entire contents of a zone.  Protection of zone contents is often a commercial or business requirement. 
  • If accepted, a NOTIFY sets the zone refresh interval to 'now'.  If there is not already a refresh cycle in progress then named will initiate one by asking for the SOA RR from its list of masters.  If there is already a refresh cycle in progress, then named will queue the new refresh request.  If there is already a queued refresh request, the new NOTIFY will be discarded. Bogus notifications can't be used to force a zone transfer from a malicious server, but could trigger a high rate of zone refresh cycles.

CVSS Score:  5.3

CVSS Vector:  CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/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:L/I:N/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. (Note that this technique may not be effective against bogus NOTIFY packets if an attacker is able to reach the target DNS server whilst using a spoofed sending address).

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 Correct Notify to NOTIFY; Update phrasing in Workarounds section; Update phrasing in Description; Correct date of similar public announcement, 29 June 2017
2.0 Public disclosure 29 June 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-01504 is the complete and official security advisory document.

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