CVE-2020-8619: An asterisk character in an empty non-terminal can cause an assertion failure in rbtdb.c

[Michael McNally]

Note:  this Security Advisory for BIND concerns a vulnerability which
can exist when a zone contains an empty non-terminal record whose label
contains an asterisk character ("*").  If you are not familiar with the
idea of "empty non-terminals", you might wish to read this article in
our Knowledge Base: https://kb.isc.org/docs/what-is-an-empty-non-terminal

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CVE:                 CVE-2020-8619
Document version:    2.0
Posting date:        17 June 2020
Program impacted:    BIND
Versions affected:   BIND 9.11.14 -> 9.11.19, BIND 9.14.9 -> 9.14.12,
                     BIND 9.16.0 -> 9.16.3.  Also, versions 9.11.14-S1 ->
                     9.11.19-S1 of BIND Supported Preview Edition
Severity:            Medium

Exploitable:

   Remotely, but only if records matching a certain pattern are
   present in a zone being served.

Description:

   The asterisk character ("*") is allowed in DNS zone files, where
   it is most commonly present as a wildcard at a terminal node of
   the Domain Name System graph. However, the RFCs do not require
   and BIND does not enforce that an asterisk character be present
   only at a terminal node.

   A problem can occur when an asterisk is present in an empty
   non-terminal location within the DNS graph. If such a node exists,
   after a series of queries, named can reach an inconsistent state
   that results in the failure of an assertion check in rbtdb.c,
   followed by the program exiting due to the assertion failure.

Impact:

   Unless a nameserver is providing authoritative service for one
   or more zones and at least one zone contains an empty non-terminal
   entry containing an asterisk ("*") character, this defect cannot
   be encountered.

   A would-be attacker who is allowed to change zone content could
   theoretically introduce such a record in order to exploit this
   condition to cause denial of service, though we consider the use
   of this vector unlikely because any such attack would require a
   significant privilege level and be easily traceable.

CVSS Score:          4.3
CVSS Vector:         AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C

For more information on the Common Vulnerability Scoring System and
to obtain your specific environmental score please visit:
https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator?vector=AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C&version=3.1.

Workarounds:

   None

Active exploits:

   We are not aware of any active exploits.

Solution:

   Upgrade to the patched release most closely related to your
   current version of BIND:

   -  BIND 9.11.20
   -  BIND 9.16.4

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

   -  BIND 9.11.20-S1

Document revision history:

   1.0 Early Notification, 10 June 2020
   1.1 Corrected "Versions affected" to list Supported Preview
       Edition releases, 17 June 2020
   2.0 Public disclosure, 17 June 2020

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 at isc.org. To report a new issue, please
encrypt your message using security-officer at isc.org's PGP key which
can be found here: https://www.isc.org/pgpkey/. If you are unable
to use encrypted email, you may also report new issues at:
https://www.isc.org/reportbug/.

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/download/.)

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 at https://kb.isc.org/docs/aa-00861.

The Knowledgebase article https://kb.isc.org/docs/cve-2020-8619 is
the complete and official security advisory document.

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