CVE-2020-8621: Attempting QNAME minimization after forwarding can lead to an assertion failure in resolver.c
Document version: 2.0
Posting date: 20 August 2020
Program impacted: BIND
Versions affected: BIND 9.14.0 -> 9.16.5, 9.17.0 -> 9.17.3
While query forwarding and QNAME minimization are mutually incompatible, BIND did sometimes allow QNAME minimization when continuing with recursion after 'forward first' did not result in an answer. In these cases the data used by QNAME minimization might be inconsistent, leading to an assertion failure, causing the server to exit.
If a server is configured with both QNAME minimization and 'forward first' then an attacker who can send queries to it may be able to trigger the condition that will cause the server to crash.
Servers that 'forward only' are not affected.
CVSS Score: 6.7
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:P/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:P/RL:O/RC:C&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 9.16.6
- BIND 9.17.4
Acknowledgments: ISC would like to thank Joseph Gullo for bringing this vulnerability to our attention.
Document revision history:
1.0 Early Notification, 12 August 2020
1.1 Updated Posting Date, 17 August 2020
2.0 Public Announcement, 20 August 2020
See our BIND 9 Security Vulnerability Matrix for a complete listing of security vulnerabilities and versions affected.
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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-2020-8621 is the complete and official security advisory document.
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