CVE: CVE-2021-25214
Document version: 2.0
Posting date: 28 April 2021
Program impacted: BIND
Versions affected: BIND 9.8.5 -> 9.8.8, 9.9.3 -> 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 9 Supported Preview Edition, as well
as release versions 9.17.0 -> 9.17.11 of the BIND 9.17
development branch
Severity: Medium
Exploitable:
Remotely, if a target server accepts zone transfers from a
potential attacker.
Description:
Incremental zone transfers (IXFR) provide a way of transferring
changed portion(s) of a zone between servers. An IXFR stream
containing SOA records with an owner name other than the transferred
zone's apex may cause the receiving named server to inadvertently
remove the SOA record for the zone in question from the zone
database. This leads to an assertion failure when the next SOA
refresh query for that zone is made.
Impact:
When a vulnerable version of named receives a malformed IXFR
triggering the flaw described above, the named process will
terminate due to a failed assertion the next time the transferred
secondary zone is refreshed.
CVSS Score: 6.5
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/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:L/UI:N/S:U/C:N/I:N/A:H&version=3.1.
Workarounds:
Disabling incremental zone transfers (IXFR) by setting request-ixfr
no; in the desired configuration block (options, zone, or server)
prevents the failing assertion from being evaluated.
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 Greg Kuechle of SaskTel 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-offi...@isc.org. To report a new issue, please
encrypt your message using security-offi...@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-2021-25214
is the complete and official security advisory document.
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