CVE-2025-40777

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.
ProviderTypeBase ScoreAtk. VectorAtk. ComplexityPriv. RequiredVector
NISTNIST
7.5 HIGH
NETWORK
LOW
NONE
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
iscCNA
7.5 HIGH
NETWORK
LOW
NONE
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Awaiting analysis
This vulnerability is currently awaiting analysis.
Base Score
CVSS 3.x
EPSS Score
Percentile: Unknown
Debian logo
Debian Releases
Debian Product
Codename
bind9
bullseye
vulnerable
bullseye (security)
vulnerable
bookworm
vulnerable
bookworm (security)
vulnerable
trixie
vulnerable
sid
1:9.20.11-1
fixed
Ubuntu logo
Ubuntu Releases
Ubuntu Product
Codename
bind9
plucky
Fixed 1:9.20.4-3ubuntu1.2
released
noble
not-affected
jammy
not-affected
focal
not-affected
bionic
not-affected
xenial
not-affected
trusty
not-affected
bind9-libs
plucky
dne
noble
dne
jammy
needs-triage
focal
needs-triage
isc-dhcp
plucky
needs-triage
noble
needs-triage
jammy
not-affected
focal
not-affected
bionic
needs-triage
xenial
not-affected
trusty
not-affected
Common Weakness Enumeration
Vulnerability Media Exposure
References
https://kb.isc.org/docs/cve-2025-40777