{"document":{"category":"csaf_vex","csaf_version":"2.0","distribution":{"text":"TuxCare License Agreement","tlp":{"label":"WHITE","url":"https://www.first.org/tlp/"}},"lang":"en","notes":[{"category":"legal_disclaimer","text":"This content is licensed under the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/). If you distribute this content, or a modified version of it, you must provide attribution to Cloud Linux Inc. and provide a link to the original.","title":"Terms of Use"}],"publisher":{"category":"vendor","contact_details":"https://tuxcare.com/contact/","name":"TuxCare","namespace":"https://tuxcare.com/"},"references":[{"category":"self","summary":"Canonical URL","url":"https://security.tuxcare.com/csaf/v2/els_os/ubuntu20.04els/vex/2026/cve-2026-11721-els_os-ubuntu20_04els.json"}],"title":"Security update on CVE-2026-11721","tracking":{"current_release_date":"2026-10-15T19:15:31Z","generator":{"date":"2026-10-15T19:15:31Z","engine":{"name":"pyCSAF"}},"id":"CVE-2026-11721-ELS_OS-UBUNTU20.04ELS","initial_release_date":"2026-07-22T15:16:00Z","revision_history":[{"date":"2026-07-22T15:16:00Z","number":"1","summary":"Initial version"},{"date":"2026-10-13T10:12:23Z","number":"2","summary":"Official Publication"},{"date":"2026-10-13T16:56:12Z","number":"3","summary":"Update 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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).\nThis 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.","title":"Vulnerability description"}],"product_status":{"known_affected":["Ubuntu-20:bind9-1:9.18.30-0ubuntu0.20.04.2.amd64","Ubuntu-20:bind9-dnsutils-1:9.18.30-0ubuntu0.20.04.2.amd64","Ubuntu-20:bind9-doc-1:9.18.30-0ubuntu0.20.04.2.all","Ubuntu-20:bind9-host-1:9.18.30-0ubuntu0.20.04.2.amd64","Ubuntu-20:bind9-libs-1:9.18.30-0ubuntu0.20.04.2.amd64","Ubuntu-20:bind9-utils-1:9.18.30-0ubuntu0.20.04.2.amd64","Ubuntu-20:bind9utils-1:9.18.30-0ubuntu0.20.04.2.all","Ubuntu-20:dnsutils-1:9.18.30-0ubuntu0.20.04.2.all"],"under_investigation":["Ubuntu-20:bind9-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els2.amd64","Ubuntu-20:bind9-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els3.amd64","Ubuntu-20:bind9-dnsutils-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els2.amd64","Ubuntu-20:bind9-dnsutils-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els3.amd64","Ubuntu-20:bind9-doc-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els2.all","Ubuntu-20:bind9-doc-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els3.all","Ubuntu-20:bind9-host-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els2.amd64","Ubuntu-20:bind9-host-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els3.amd64","Ubuntu-20:bind9-libs-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els2.amd64","Ubuntu-20:bind9-libs-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els3.amd64","Ubuntu-20:bind9-utils-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els2.amd64","Ubuntu-20:bind9-utils-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els3.amd64","Ubuntu-20:bind9utils-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els2.all","Ubuntu-20:bind9utils-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els3.all","Ubuntu-20:dnsutils-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els2.all","Ubuntu-20:dnsutils-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els3.all"]},"references":[{"category":"self","summary":"Canonical URL","url":"https://cve.tuxcare.com/els/cve/CVE-2026-11721"},{"category":"external","summary":"https://downloads.isc.org/isc/bind9/9.20.26","url":"https://downloads.isc.org/isc/bind9/9.20.26"},{"category":"external","summary":"https://downloads.isc.org/isc/bind9/9.21.24","url":"https://downloads.isc.org/isc/bind9/9.21.24"},{"category":"external","summary":"https://kb.isc.org/docs/cve-2026-11721","url":"https://kb.isc.org/docs/cve-2026-11721"}],"release_date":"2026-07-22T15:16:00Z","remediations":[{"category":"no_fix_planned","date":"2026-10-13T10:58:28.591921Z","details":"This issue only applies when BIND is acting as a validating recursive resolver with synth-from-dnssec enabled; authoritative-only deployments or systems not providing recursion are unaffected. The attack is high complexity and results only in low confidentiality/integrity impact with no availability effect (CVSS 4.8), which limits practical risk. Given these narrow preconditions and the constrained impact, it can be safely deprioritized relative to vulnerabilities enabling direct compromise or broader disruption.","product_ids":["Ubuntu-20:bind9-1:9.18.30-0ubuntu0.20.04.2.amd64","Ubuntu-20:bind9-dnsutils-1:9.18.30-0ubuntu0.20.04.2.amd64","Ubuntu-20:bind9-doc-1:9.18.30-0ubuntu0.20.04.2.all","Ubuntu-20:bind9-host-1:9.18.30-0ubuntu0.20.04.2.amd64","Ubuntu-20:bind9-libs-1:9.18.30-0ubuntu0.20.04.2.amd64","Ubuntu-20:bind9-utils-1:9.18.30-0ubuntu0.20.04.2.amd64","Ubuntu-20:bind9utils-1:9.18.30-0ubuntu0.20.04.2.all","Ubuntu-20:dnsutils-1:9.18.30-0ubuntu0.20.04.2.all"]},{"category":"none_available","date":"2026-10-15T08:16:09.707473Z","details":"Affected","product_ids":["Ubuntu-20:bind9-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els2.amd64","Ubuntu-20:bind9-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els3.amd64","Ubuntu-20:bind9-dnsutils-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els2.amd64","Ubuntu-20:bind9-dnsutils-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els3.amd64","Ubuntu-20:bind9-doc-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els2.all","Ubuntu-20:bind9-doc-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els3.all","Ubuntu-20:bind9-host-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els2.amd64","Ubuntu-20:bind9-host-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els3.amd64","Ubuntu-20:bind9-libs-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els2.amd64","Ubuntu-20:bind9-libs-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els3.amd64","Ubuntu-20:bind9-utils-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els2.amd64","Ubuntu-20:bind9-utils-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els3.amd64","Ubuntu-20:bind9utils-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els2.all","Ubuntu-20:bind9utils-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els3.all","Ubuntu-20:dnsutils-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els2.all","Ubuntu-20:dnsutils-1:9.18.30-0ubuntu0.20.04.2+tuxcare.els3.all"]}]}]}