CVE: CVE-2026-3039
Title: BIND 9 server memory exhaustion during GSS-API TKEY negotiation
Document version: 2.0
Posting date: 20 May 2026
Program impacted: BIND 9
Versions affected:
BIND
- 9.0.0 -> 9.16.50
- 9.18.0 -> 9.18.48
- 9.20.0 -> 9.20.22
- 9.21.0 -> 9.21.21
BIND Supported Preview Edition
- 9.9.3-S1 -> 9.16.50-S1
- 9.18.11-S1 -> 9.18.48-S1
- 9.20.9-S1 -> 9.20.22-S1
(Versions prior to 9.11.37 were not assessed.)
Although we have not tested them individually, we believe that all EoL versions of BIND are vulnerable to this weakness.
Severity: High
Exploitable: Remotely
Description:
BIND servers that are configured to use TKEY-based authentication via GSS-API tokens are vulnerable to excessive memory consumption when receiving and processing maliciously-constructed packets. Typically these servers will be found in Active Directory integrated DNS deployments and/or Kerberos-secured DNS environments.
Impact:
An attacker can construct and send packets to a BIND server that will cause it to allocate memory that is not subsequently released. Depending on the volume and frequency of the packets received, named will eventually fail due to memory exhaustion.
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:
We are not aware of any active exploits.
Solution:
Upgrade to the patched release most closely related to your current version of BIND 9:
- 9.18.49
- 9.20.23
- 9.21.22
BIND Supported Preview Edition is a special feature preview branch of BIND provided to eligible ISC support customers.
- 9.18.49-S1
- 9.20.23-S1
Acknowledgments:
ISC would like to thank Vitaly Simonovich for bringing this vulnerability to our attention.
Document revision history:
- 1.0 Early Notification, 13 May 2026
- 1.1 Remove references to keytab (using GSS-API TKEY is sufficient for exposure), 14 May 2026
- 2.0 Public disclosure, 20 May 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 mailed to bind-security@isc.org or 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-2026-3039 is the complete and official security advisory document.
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