CVE-2021-25215: An assertion check can fail while answering queries for DNAME records that require the DNAME to be processed to resolve itself

CVE: CVE-2021-25215

Document version: 2.0

Posting date: 28 April 2021

Program impacted: BIND

Versions affected: BIND 9.0.0 -> 9.11.29, 9.12.0 -> 9.16.13, and versions BIND 9.9.3-S1 -> 9.11.29-S1 and 9.16.8-S1 -> 9.16.13-S1 of BIND Supported Preview Edition, as well as release versions 9.17.0 -> 9.17.11 of the BIND 9.17 development branch

Severity: High

Exploitable: Remotely

Description:

DNAME records, described in RFC 6672, provide a way to redirect a subtree of the domain name tree in the DNS. A flaw in the way named processes these records may trigger an attempt to add the same RRset to the ANSWER section more than once. This causes an assertion check in BIND to fail.

DNAME records are processed by both authoritative and recursive servers. For authoritative servers, the DNAME record triggering the flaw can be retrieved from a zone database. For servers performing recursion, such a record is processed in the course of a query sent to an authoritative server.

Impact:

When a vulnerable version of named receives a query for a record triggering the flaw described above, the named process will terminate due to a failed assertion check.

The vulnerability affects all currently maintained BIND 9 branches (9.11,
9.11-S, 9.16, 9.16-S, 9.17) as well as all other versions of BIND 9.

CVSS Score: 7.5

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/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://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&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 9.11.31
• BIND 9.16.15
• BIND 9.17.12

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

• BIND 9.11.31-S1
• BIND 9.16.15-S1

Acknowledgments: ISC would like to thank Siva Kakarla for bringing this vulnerability to our attention.

Document revision history:

1.0 Early Notification, 14 April 2021
1.1 Disclosure schedule change, 15 April 2021
2.0 Public disclosure, 28 April 2021

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-2021-25215 is the complete and official security advisory document.

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