Vulnerability · Published Jul 16, 2025 · Assigned by isc
CVE-2025-40777A possible assertion failure when 'stale-answer-client-timeout' is set to '0'
High 7.5
In plain English
A high-severity security flaw in BIND 9 from ISC. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 1.0% (higher than 63% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.22 | bind | 9.20.11-r0 | ALPINE-CVE-2025-40777 |
| Alpine:v3.23 | bind | 9.20.11-r0 | ALPINE-CVE-2025-40777 |
| Alpine:v3.24 | bind | 9.20.11-r0 | ALPINE-CVE-2025-40777 |
| Debian:13 | bind9 | 1:9.20.11-1 | DEBIAN-CVE-2025-40777 |
| Debian:14 | bind9 | 1:9.20.11-1 | DEBIAN-CVE-2025-40777 |
Affected products (as reported)
Weakness: CWE-617 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H