CVE-2020-8622: A truncated TSIG response can lead to an assertion failure

[Michael McNally]

CVE:                 CVE-2020-8622
Document version:    2.0
Posting date:        20 August 2020
Program impacted:    BIND
Versions affected:   BIND 9.0.0 -> 9.11.21, 9.12.0 -> 9.16.5, 9.17.0 -> 9.17.3,
                     also affects 9.9.3-S1 -> 9.11.21-S1 of the BIND Supported
                     Preview Edition
Severity:            Medium
Exploitable:         Remotely

Description:

   Attempting to verify a truncated response to a TSIG-signed request leads to
   an assertion failure.

Impact:

   An attacker on the network path for a TSIG-signed request, or operating the
   server receiving the TSIG-signed request, could send a truncated response to
   that request, triggering an assertion failure, causing the server to exit.

   Alternately, an off-path attacker would have to correctly guess when a
   TSIG-signed request was sent, along with other characteristics of the packet
   and message, and spoof a truncated response to trigger an assertion failure,
   causing the server to exit.

CVSS Score: 5.9
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H/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:N/A:H/E:P/RL:O/RC:C&version=3.1.

Workarounds:

   No workarounds known.

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 9.11.22
   - 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 Dave Feldman, Jeff Warren, and Joel Cunningham  of
   Oracle 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-2020-8622 is the complete
and official security advisory document.

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