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.

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