CVE-2026-11721

Cache poisoning possible with label count discrepancy, RRSIG, and wildcards

State: Published
Severity: 7.5 High
Published: Jul 22, 2026
Updated: Jul 22, 2026
Reserved: Jun 9, 2026

Description

It is possible for an attacker's zone to respond to a query with an RRSIG that has a smaller number of labels than the zone in which the RRSIG is contained. This causes `named` to produce a wildcard name for a zone that is shorter than the attacker's zone, which can result in cache poisoning. For this attack to have any effect, the resolver under attack must have set `synth-from-dnssec yes;` (which is the default). This issue affects BIND 9 versions 9.11.0 through 9.18.50, 9.20.0 through 9.20.24, 9.21.0 through 9.21.23, 9.11.3-S1 through 9.18.50-S1, and 9.20.9-S1 through 9.20.24-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:H/A:N	isc

Weaknesses

CWE-1284 Improper Validation of Specified Quantity in Input

Affected Products

Product	Versions
BIND 9ISC	9.11.0 through 9.18.50Affected 9.20.0 through 9.20.24Affected 9.21.0 through 9.21.23Affected 9.11.3-S1 through 9.18.50-S1Affected 9.20.9-S1 through 9.20.24-S1Affected

References

CVE-2026-11721vendor-advisory
https://downloads.isc.org/isc/bind9/9.20.26patch
https://downloads.isc.org/isc/bind9/9.21.24patch

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