High severity · published Jul 16, 2025
CVE-2025-40777
A possible assertion failure when 'stale-answer-client-timeout' is set to '0'
7.5
CVSS
1%
EPSS
No
On KEV
Description
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)1.0% · higher than 63% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
B9
BIND 9 · ISC
9.20.0 through 9.20.10; 9.21.0 through 9.21.9; 9.20.9-S1 through 9.20.10-S1 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-40777
CVE.org
https://www.cve.org/CVERecord?id=CVE-2025-40777
kb.isc.org
https://kb.isc.org/docs/cve-2025-40777
www.openwall.com
http://www.openwall.com/lists/oss-security/2025/07/16/6
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