CVE-2025-40777

A possible assertion failure when 'stale-answer-client-timeout' is set to '0'

State: Published
Severity: 7.5 High
Published: Jul 16, 2025
Updated: Nov 4, 2025
Reserved: Apr 16, 2025

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.

Scores

CVSS	Score	Vector	Source
3.1	7.5 High	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H	isc

Weaknesses

CWE-617 Reachable Assertion

Affected Products

Product	Versions
BIND 9ISC	9.20.0 through 9.20.10Affected 9.21.0 through 9.21.9Affected 9.20.9-S1 through 9.20.10-S1Affected 9.18.0 through 9.18.37Not affected 9.18.11-S1 through 9.18.37-S1Not affected

References

CVE-2025-40777vendor-advisory
http://www.openwall.com/lists/oss-security/2025/07/16/6

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