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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2021.2819 ISC Security Vulnerability Impacting BIND 19 August 2021 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: BIND Publisher: ISC Operating System: Windows UNIX variants (UNIX, Linux, OSX) Impact/Access: Denial of Service -- Remote/Unauthenticated Resolution: Patch/Upgrade CVE Names: CVE-2021-25218 Original Bulletin: https://kb.isc.org/v1/docs/cve-2021-25218 - --------------------------BEGIN INCLUDED TEXT-------------------- CVE: CVE-2021-25218 Document version: 2.0 Posting date: 18 August 2021 Program impacted: BIND Versions affected: BIND 9.16.19, 9.17.16. Also, version 9.16.19-S1 of BIND Supported Preview Edition Severity: High Exploitable: Remotely Description: If named attempts to respond over UDP with a response that is larger than the current effective interface maximum transmission unit (MTU), and if response-rate limiting (RRL) is active, an assertion failure is triggered (resulting in termination of the named server process). There are two ways for named to exceed the interface MTU: Direct configuration in named.conf setting max-udp-size to a value larger than the interface's MTU, or Path MTU discovery (PMTUD) informing the IP stack that it should use a smaller MTU for the interface and destination than the default max-udp-size value of 1232. Some operating systems allow packets received via other protocols to affect PMTUD values for DNS over UDP. While RRL is not enabled by default for user-defined views or the built-in default INTERNET (IN) class view, "_default", the built-in default CHAOS (CH) class view, "_bind", does have RRL enabled. Note that while this defect can be triggered through misconfiguration or by deliberate exploitation, it can also arise during normal operating conditions, even with hardened PMTUD settings. Impact: When a vulnerable version of named receives a query under the circumstances described above, the named process will terminate due to a failed assertion check. The vulnerability ONLY affects BIND 9 releases 9.16.19, 9.17.16, and release 9.16.19-S1 of the BIND Supported Preview Edition. 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=CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H&version=3.1 Workarounds: Disabling RRL in all views, including the built-in CHAOS class view "_bind", prevents the faulty assertion from being reached. This can be done by removing all existing rate-limit statements from named.conf, and defining a replacement for the default CHAOS view: view override_bind chaos { recursion no; notify no; allow-new-zones no; max-cache-size 2M; zone "version.bind" chaos { type primary; database "_builtin version"; }; zone "hostname.bind" chaos { type primary; database "_builtin hostname"; }; zone "authors.bind" chaos { type primary; database "_builtin authors"; }; zone "id.server" chaos { type primary; database "_builtin id"; }; }; 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 9.16.20 - BIND 9.17.17 BIND Supported Preview Edition is a special feature preview branch of BIND provided to eligible ISC support customers. - BIND 9.16.20-S1 Document revision history: 1.0 Advance notification to customers, 11 August 2020 2.0 Public disclosure, 18 August 2020 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-2021-25218 is the complete and official security advisory document. Legal Disclaimer: Internet Systems Consortium (ISC) is providing this notice on an "AS IS" basis. No warranty or guarantee of any kind is expressed in this notice and none should be implied. ISC expressly excludes and disclaims any warranties regarding this notice or materials referred to in this notice, including, without limitation, any implied warranty of merchantability, fitness for a particular purpose, absence of hidden defects, or of non-infringement. Your use or reliance on this notice or materials referred to in this notice is at your own risk. ISC may change this notice at any time. A stand-alone copy or paraphrase of the text of this document that omits the document URL is an uncontrolled copy. Uncontrolled copies may lack important information, be out of date, or contain factual errors. _______________________________________________ - --------------------------END INCLUDED TEXT-------------------- You have received this e-mail bulletin as a result of your organisation's registration with AusCERT. The mailing list you are subscribed to is maintained within your organisation, so if you do not wish to continue receiving these bulletins you should contact your local IT manager. If you do not know who that is, please send an email to auscert@auscert.org.au and we will forward your request to the appropriate person. NOTE: Third Party Rights This security bulletin is provided as a service to AusCERT's members. 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Previous advisories and external security bulletins can be retrieved from: https://www.auscert.org.au/bulletins/ =========================================================================== Australian Computer Emergency Response Team The University of Queensland Brisbane Qld 4072 Internet Email: auscert@auscert.org.au Facsimile: (07) 3365 7031 Telephone: (07) 3365 4417 (International: +61 7 3365 4417) AusCERT personnel answer during Queensland business hours which are GMT+10:00 (AEST). On call after hours for member emergencies only. =========================================================================== -----BEGIN PGP SIGNATURE----- Comment: http://www.auscert.org.au/render.html?it=1967 iQIVAwUBYR3fCuNLKJtyKPYoAQjEEBAAonpgMFAUBuoQo615iFeHHodoR9a1roLw o/XEmlFMeDXh2NGrmVa25/CQ60XGhMM4ryJwUermOLsPtbfzu3uFTZQECOh6+YQk ohagFpSFBboEpDBHWomb9vWvfmoI33km0qdUKhG3UhAJ/cSwqYrX6ftK2HNWy8Jt tl8KfjR1lmTfV1vizFSUxvJY4c9uFahwtaLSWmsxN9rP63wOswcJ98M8ZqK4+mv1 Sc3cNuUFsEEA2PR9TsSHKoDLn5ZnyMHFiX5gupEouD8/w0QYO50loKtVbEvJTKj+ qkG1EN1+EiIfTm8nDDdZnQMoTPNOk6E5z9aglrO8XspB13XOJvRWhTrk6Ud/IcPi /QqBhDuRuUzA/OFsc9FvukNEApvbt2rX0ban4+GgGzn5CaSSDxN3btFbvPOdP5qO QJROM53NtXk19sY0iLZnga7AObVuhdRibB+qKImq0rkVX6QIzvkNf+a1BeoIaard WZSFmn+LVRgXZgl9WZL+Jr0axcPKmjR1LwjcGxwVqVZQfjqtAhnYCiwLQ6IPXmkn BIdcXw3IOiiUyFIXArqUhi2bqPdozFvE936tqLlu3232/MkZJKOTbtXqXjyNFYkQ iJLkQRKyIBcngr/CDhZBg4Tv2WCHQ9KGLX+gMzjEF3WNT67OqrWY6VVd6Nv9/PQE GkVLzryh5As= =vMj5 -----END PGP SIGNATURE-----