CVE: CVE-2026-11605
Title: Unnecessary validation of DNSSEC signed records
Document version: 2.0
Posting date: 22 July 2026
Program impacted: BIND 9
Versions affected:
BIND
- 9.20.0 -> 9.20.24
- 9.21.0 -> 9.21.23
BIND Supported Preview Edition
- 9.20.9-S1 -> 9.20.24-S1
Severity: High
Exploitable: Remotely
Description:
The issue is a resource exhaustion vulnerability associated with DNSSEC validation. BIND always validates all RRSIG records in an answer, even if they are not strictly needed. A query to an authoritative server/zone which returns many valid but superfluous RRSIG records causes the validator to waste disproportionate CPU time.
Impact:
Exhaustion of CPU resources.
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=AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H&version=3.1.
Workarounds:
No workarounds known.
Active exploits:
This flaw was discovered in internal testing. We are not aware of any active exploits.
Solution:
Upgrade to the patched release most closely related to your current version of BIND 9:
- 9.20.26
- 9.21.24
BIND Supported Preview Edition is a special feature preview branch of BIND provided to eligible ISC support customers.
- 9.20.26-S1
Document revision history:
- 1.0 Early Notification, 15 July 2026
- 1.1 Revised the list of fixed versions, 20 July 2026
- 2.0 Public disclosure, 22 July 2026
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 be posted as confidential GitLab issues at:
https://gitlab.isc.org/isc-projects/bind9/-/issues/new?issue[confidential]=true
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-2026-11605 is the complete and official security advisory document.
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