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CVE-2022-0635: DNAME insist with synth-from-dnssec enabled
CVE: CVE-2022-0635
Document version: 2.0
Posting date: 16 March 2022
Program impacted: BIND
Versions affected: BIND 9.18.0
Severity: High
Exploitable: Remotely
Description:
We refactored the RFC 8198 Aggressive Use of DNSSEC-Validated Cache feature (synth-from-dnssec) for the new BIND 9.18.0 stable release, and changed the default so that is now automatically enabled for dnssec-validating resolvers. Subsequently it was found that repeated patterns of specific queries to servers with this feature enabled could cause an INSIST failure in query.c:query_dname which causes named to terminate unexpectedly.
The vulnerability affects BIND resolvers running 9.18.0 that have both dnssec-validation and synth-from-dnssec enabled. (Note that dnssec-validation auto;
is the default setting unless configured otherwise in named.conf
and that enabling dnssec-validation automatically enables synth-from-dnssec
unless explicitly disabled)
Impact:
When a vulnerable version of named receives a series of specific queries, the named process will eventually terminate due to a failed assertion check.
CVSS Score: 7.0
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:F/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:F/RL:O/RC:C&version=3.1.
Workarounds:
The failure can be avoided by adding this option to named.conf:
synth-from-dnssec no;
However we do not recommend disabling this feature other than as a temporary workaround because it provides protection from pseudo-random-subdomain attacks against DNSSEC-signed zones.
Active exploits:
We are not aware of any active exploits.
Solution:
- Users of BIND 9.18.0 should upgrade to BIND 9.18.1
Acknowledgments:
ISC would like to thank Vincent Levigneron of AFNIC for reporting this issue to us and for verifying the fix and workaround.
Document revision history:
1.0 Early Notification, 9 March 2022
2.0 Public disclosure, 16 March 2022
Related documents:
See Operational Notification: synth-from-dnssec may cause slow resolution on resolvers under certain cache conditions for more information regarding early BIND support for RFC 8198 Aggressive Use of DNSSEC-Validated Cache and our recommendation that this feature be disabled until versions of BIND were made available which contain an improvement to the synth-from-dnssec feature.
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-2022-0635 is the complete and official security advisory document.
Legal Disclaimer:
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