CVE: CVE-2025-40775
Title: DNS message with invalid TSIG causes an assertion failure
Document version: 2.0
Posting date: 21 May 2025
Program impacted: BIND 9
Versions affected:
BIND
- 9.20.0 -> 9.20.8
- 9.21.0 -> 9.21.7
(Versions prior to 9.18.0 were not assessed.)
Severity: High
Exploitable: Remotely
Description:
When an incoming DNS protocol message includes a Transaction Signature (TSIG), BIND always checks it. If the TSIG contains an invalid value in the algorithm field, BIND immediately aborts with an assertion failure.
Impact:
Denial-of-service. By sending specific messages to the server, an attacker can cause named to terminate unexpectedly.
-
Authoritative servers are affected by this vulnerability.
-
Resolvers are affected by this vulnerability.
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:
- 9.20.9
- 9.21.8
Document revision history:
- 1.0 Early Notification, 14 May 2025
- 1.1 Clarified the list of affected versions, 19 May 2025
- 2.0 Public disclosure, 21 May 2025
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-2025-40775 is the complete and official security advisory document.
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