CVE-2018-5736: Multiple transfers of a zone in quick succession can cause an assertion failure in rbtdb.c

[Michael McNally]

CVE:                 CVE-2018-5736
Document Version:    2.0
Posting date:        18 May 2018
Program Impacted:    BIND
Versions affected:   9.12.0 and 9.12.1
Severity:            Medium
Exploitable:         Remotely, if an attacker can trigger a zone transfer

Description:

   An error in zone database reference counting can lead to an
   assertion failure if a server which is running an affected version
   of BIND attempts several transfers of a slave zone in quick
   succession.

   This defect could be deliberately exercised by an attacker who
   is permitted to cause a vulnerable server to initiate zone
   transfers (for example: by sending valid NOTIFY messages), causing
   the named process to exit after failing the assertion test.

Impact:

   Authoritative servers that serve slave zones are vulnerable to
   potential denial of service if all of the following are true:

   +  they are running an affected version of BIND (BIND 9.12.0
      or 9.12.1)
   +  at least one of the zones for which they are providing service
      is of type "slave"
   +  they permit NOTIFY messages from any source.

CVSS Score:          5.3
CVSS Vector:         CVSS:3.0/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

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

Workarounds:

   For servers which must receive notifies to keep slave zone
   contents current, no complete workarounds are known although
   restricting BIND to only accept NOTIFY messages from authorized
   sources can greatly mitigate the risk of attack.

Active exploits:

   No known active exploits.

Solution:

   The reference counting error which can be exploited in this
   vulnerability is present in only two public release versions of
   BIND, 9.12.0 and 9.12.1.  If you are running an affected version
   then upgrade to BIND 9.12.1-P1

Acknowledgements:

   ISC would like to thank SWITCH for informing us of this vulnerability.

Document Revision History:

   1.0 Advance Notification 09 May 2018
   2.0 Public Disclosure 18 May 2018

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.

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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

This Knowledge Base article https://kb.isc.org/article/AA-01602 is
the complete and official security advisory document.

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