{"id":"CVE-2026-33219","aliases":["BIT-nats-2026-33219","GHSA-8r68-gvr4-jh7j","GO-2026-4831"],"url":"https://o3.security/vulnerability/CVE-2026-33219","summary":"NATS is vulnerable to pre-auth DoS through WebSockets client service","details":"### Background\n\nNATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing.\n\nThe nats-server offers a WebSockets client service, used in deployments where browsers are the NATS clients.\n\n### Problem Description\n\nA malicious client which can connect to the WebSockets port can cause unbounded memory use in the nats-server before authentication; this requires sending a corresponding amount of data.\n\nThis is a milder variant of [NATS-advisory-ID 2026-02](https://advisories.nats.io/CVE/secnote-2026-02.txt) (aka CVE-2026-27571; GHSA-qrvq-68c2-7grw).\nThat earlier issue was a compression bomb, this vulnerability is not. Attacks against this new issue thus require significant client bandwidth.\n\n### Affected Versions\n\nAny version before v2.12.6 or v2.11.15\n\n### Workarounds\n\nDisable websockets if not required for project deployment.","published":"2026-03-25T19:55:28.363Z","modified":"2026-09-11T03:30:18.697050152Z","cvss":{"score":5.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"},"epss":{"score":0.00525,"percentile":0.43322,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/nats-io/nats-server/v2","fixedVersion":"2.11.15"},{"ecosystem":"Go","name":"github.com/nats-io/nats-server/v2","fixedVersion":"2.12.6"},{"ecosystem":"Go","name":"github.com/nats-io/nats-server","fixedVersion":null}],"fix":null,"references":[{"type":"WEB","url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33219.json"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:21769"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:22347"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:23345"},{"type":"ADVISORY","url":"https://access.redhat.com/security/cve/CVE-2026-33219"},{"type":"ADVISORY","url":"https://advisories.nats.io/CVE/secnote-2026-02.txt"},{"type":"ADVISORY","url":"https://advisories.nats.io/CVE/secnote-2026-11.txt"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33219.json"},{"type":"ADVISORY","url":"https://github.com/advisories/GHSA-qrvq-68c2-7grw"},{"type":"ADVISORY","url":"https://github.com/nats-io/nats-server/security/advisories/GHSA-8r68-gvr4-jh7j"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-33219"},{"type":"REPORT","url":"https://bugzilla.redhat.com/show_bug.cgi?id=2451445"},{"type":"PACKAGE","url":"https://github.com/nats-io/nats-server"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-11T03:30:18.697050152Z"}}