CVE-2017-3138: named exits with a REQUIRE assertion failure if it receives a null command string on its control channel

[Michael McNally]

CVE:                 CVE-2017-3138
Document Version:    2.0
Posting date:        12 April 2017
Program Impacted:    BIND
Versions affected:   9.9.9->9.9.9-P7, 9.9.10b1->9.9.10rc2,
9.10.4->9.10.4-P7,
                     9.10.5b1->9.10.5rc2, 9.11.0->9.11.0-P4,
                     9.11.1b1->9.11.1rc2, 9.9.9-S1->9.9.9-S9
Severity:            Medium
Exploitable:         Remotely, from hosts that are within the ACL permitted
                     access to the control channel

Description:

   named contains a feature which allows operators to issue commands
   to a running server by communicating with the server process
   over a control channel, using a utility program such as rndc.

   A regression introduced in a recent feature change has created
   a situation under which some versions of named can be caused
   to exit with a REQUIRE assertion failure if they are sent a
   null command string.

Impact:

   The BIND control channel is not configured by default, but when
   configured will accept commands from those IP addresses that
   are specified in its access control list and/or from clients
   which present the proper transaction key.  Using this defect,
   an attacker can cause a running server to stop if they can get
   it to accept control channel input from them.  In most instances
   this is not as bad as it sounds, because existing commands
   permitted over the control channel (i.e. "rndc stop") can already
   be given to cause the server to stop.

   However, BIND 9.11.0 introduced a new option to allow "read
   only" commands over the command channel.  Using this restriction,
   a server can be configured to limit specified clients to giving
   control channel commands which return information only (e.g.
   "rndc status") without affecting the operational state of the
   server.  The defect described in this advisory, however, is not
   properly stopped by the "read only" restriction, in essence
   permitting a privilege escalation allowing a client which should
   only be permitted the limited set of "read only" operations to
   cause the server to stop execution.

CVSS Score:          6.5
CVSS Vector:         CVSS:3.0/AV:N/AC:L/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:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Workarounds:

   None.  However, in a properly configured server, access to the
   control channel should already be limited by either network
   ACLs, TSIG keys, or both.

Active exploits:

   No known active exploits

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 9.9.9-P8
   -  BIND 9 version 9.10.4-P8
   -  BIND 9 version 9.11.0-P5

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

   -  BIND 9 version 9.9.9-S10

   New development releases of BIND are also available which
   contain the fix for this vulnerability.

   -  BIND 9 version 9.9.10rc3
   -  BIND 9 version 9.10.5rc3
   -  BIND 9 version 9.11.1rc3

Acknowledgements:

   ISC would like to thank Mike Lalumiere of Dyn, Inc., for bringing
   this issue to our attention.

Document Revision History:

   1.0 Advance Notification 20 March 2017
   1.1 Revised Acknowledgements and Versions Affected 22 March 2017
   1.2 Added mention of maintenance releases to the Solution section
       31 March 2017
   2.0 Public Announcement 12 April 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.

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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-01471 is
the complete and official security advisory document.

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