CVE-2020-8624: update-policy rules of type "subdomain" are enforced incorrectly

[Michael McNally]

CVE:                 CVE-2020-8624
Document version:    2.0
Posting date:        20 August 2020
Program impacted:    BIND
Versions affected:   BIND 9.9.12 -> 9.9.13, 9.10.7 -> 9.10.8,
                     9.11.3 -> 9.11.21, 9.12.1 -> 9.16.5, 9.17.0 -> 9.17.3,
                     also affects 9.9.12-S1 -> 9.9.13-S1,
                     9.11.3-S1 -> 9.11.21-S1 of the BIND 9 Supported
                     Preview Edition
Severity:            Low
Exploitable:         Remotely

Description:

   Change 4885 inadvertently caused "update-policy" rules of type "subdomain"
   to be treated as if they were of type "zonesub", allowing updates to all
   parts of the zone along with the intended subdomain.

Impact:

   An attacker who has been granted privileges to change a specific subset of
   the zone's content could abuse these unintended additional privileges to
   update other contents of the zone.

CVSS Score: 3.9
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N/E:P/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:L/UI:N/S:U/C:N/I:L/A:N/E:P/RL:O/RC:C&version=3.1.

Workarounds:

   No workarounds known.

Active exploits:

   We are not aware of any active exploits but the issue has been
   described on a public bug tracker for a Linux distribution.

Solution:

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

   - BIND 9.11.22
   - BIND 9.16.6
   - BIND 9.17.4

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

   - BIND 9.11.22-S1

Acknowledgments:

   ISC would like to thank Joop Boonen of credativ GmbH for bringing this
   vulnerability to our attention.

Document revision history:

1.0 Early Notification, 12 August 2020
1.1 Updated Posting Date, 17 August 2020
2.0 Public Announcement, 20 August 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-2020-8624 is the complete
and official security advisory document.

Legal Disclaimer:

   Internet Systems Consortium (ISC) is providing this notice on an "AS IS"
   basis. No warranty or guarantee of any kind is expressed in this notice and
   none should be implied. ISC expressly excludes and disclaims any warranties
   regarding this notice or materials referred to in this notice, including,
   without limitation, any implied warranty of merchantability, fitness for a
   particular purpose, absence of hidden defects, or of non-infringement. Your
   use or reliance on this notice or materials referred to in this notice is at
   your own risk. ISC may change this notice at any time. A stand-alone copy or
   paraphrase of the text of this document that omits the document URL is an
   uncontrolled copy. Uncontrolled copies may lack important information, be
   out of date, or contain factual errors.