CVE-2021-25215: An assertion check can fail while answering queries for DNAME records that require the DNAME to be processed to resolve itself
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
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.
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.
No workarounds known.
We are not aware of any active exploits.
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
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 firstname.lastname@example.org. To report a new issue, please encrypt your message using email@example.com'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/.
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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