CVE-2025-40777
July 16, 2025
If a "named" caching resolver is configured with "serve-stale-enable" "yes", and with "stale-answer-client-timeout" set to "0" (the only allowable value other than "disabled"), and if the resolver, in the process of resolving a query, encounters a CNAME chain involving a specific combination of cached or authoritative records, the daemon will abort with an assertion failure.
This issue affects BIND 9 versions 9.20.0 through 9.20.10, 9.21.0 through 9.21.9, and 9.20.9-S1 through 9.20.10-S1.
Affected Packages
https://github.com/isc-projects/bind9.git (GITHUB):
Affected version(s) >=v9.21.0 <v9.21.10Fix Suggestion:
Update to version v9.21.10https://github.com/isc-projects/bind9.git (GITHUB):
Affected version(s) >=v9.20.0 <v9.20.11Fix Suggestion:
Update to version v9.20.11Additional Notes
The description of this vulnerability differs from MITRE.
Related Resources (2)
Do you need more information?
Contact UsCVSS v4
Base Score:
8.7
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
NONE
User Interaction
NONE
Vulnerable System Confidentiality
NONE
Vulnerable System Integrity
NONE
Vulnerable System Availability
HIGH
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
7.5
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
HIGH
Weakness Type (CWE)
Reachable Assertion
EPSS
Base Score:
0.01
