What’s Vulnerable › Vulnerabilities

CVE-2026-11721: Cache poisoning possible with label count discrepancy, RRSIG, and wildcards

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-22 · updated 2026-10-24
• Weakness: CWE-1284

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.

Affected products

• ISC BIND: from 9.11.0 through 9.18.50; from 9.20.0 through 9.20.24; from 9.21.0 through 9.21.23; from 9.11.3-S1 through 9.18.50-S1; from 9.20.9-S1 through 9.20.24-S1

References

• https://downloads.isc.org/isc/bind9/9.20.26
• https://downloads.isc.org/isc/bind9/9.21.24
• https://kb.isc.org/docs/cve-2026-11721

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