CVE-2025-40777CWE-617

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

High · published July 16, 2025

CVSS v3.1
7.5
EPSS
1%
Percentile
63.2
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
7.5 · HIGH
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS v4.0
Not supplied
EPSS
0.01025 · 63.2th percentile
Weakness
CWE-617 · Reachable Assertion
Published
2025-07-16T17:38Z
EPSS history
Timeline
  • 16 JUL 17:38Z
    A possible assertion failure when 'stale-answer-client-timeout' is set to '0'
    cvelistv5