CVE-2026-11721: ISC BIND 9

High severity, CVSS 7.5. EPSS: 0.4% chance of exploitation in the next 30 days.

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.

Affected products

• ISC BIND 9: from 9.11.0, up to and including 9.18.50; from 9.20.0, up to and including 9.20.24; from 9.21.0, up to and including 9.21.23; from 9.11.3-S1, up to and including 9.18.50-S1; from 9.20.9-S1, up to and including 9.20.24-S1

Published 2026-07-22. Last modified 2026-07-22.