CVE-2020-8621: Attempting QNAME minimization after forwarding can lead to an assertion failure in resolver.c
  • 20 Aug 2020
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CVE-2020-8621: Attempting QNAME minimization after forwarding can lead to an assertion failure in resolver.c

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CVE: CVE-2020-8621

Document version: 2.0

Posting date: 20 August 2020

Program impacted: BIND

Versions affected: BIND 9.14.0 -> 9.16.5, 9.17.0 -> 9.17.3

Severity: Medium

Exploitable: Remotely

Description:

While query forwarding and QNAME minimization are mutually incompatible, BIND did sometimes allow QNAME minimization when continuing with recursion after 'forward first' did not result in an answer. In these cases the data used by QNAME minimization might be inconsistent, leading to an assertion failure, causing the server to exit.

Impact:

If a server is configured with both QNAME minimization and 'forward first' then an attacker who can send queries to it may be able to trigger the condition that will cause the server to crash.

Servers that 'forward only' are not affected.

CVSS Score: 6.7

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/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:N/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 9.16.6
  • BIND 9.17.4

Acknowledgments: ISC would like to thank Joseph Gullo 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@isc.org. To report a new issue, please encrypt your message using security-officer@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-2020-8621 is the complete and official security advisory document.

Legal Disclaimer:

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