Vulnerability in Isc Bind 9
CVE-2026-11721
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.
EPSS: 0.004 (32.7th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N.
Affected products
- Isc Bind 9 — versions 9.11.0, 9.20.0, 9.21.0
Weakness classification (CWE)
References
- security-officer@isc.org (vendor-advisory)
- security-officer@isc.org (patch)
- security-officer@isc.org (patch)
Frequently asked questions
- What is CVE-2026-11721?
- CVE-2026-11721 is a high-severity vulnerability in Isc Bind 9, classified under Improper Validation of Specified Quantity in Input. CVSS score: 7.5/10. Published 2026-07-22.
- How severe is CVE-2026-11721?
- High severity. CVSS v3 base score is 7.5 out of 10.