{"id":"CVE-2026-33219","title":"NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system","summary":"NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions 2.11.15 and 2.12.6, a malicious client which can connect to the WebSockets port can cause unbounded memory use in the nats-…","severity":"medium","cvss":5.3,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","cwe":["CWE-770"],"vendor":"linuxfoundation","product":"nats-server","affected":["nats-server < 2.11.15","nats-server >= 2.12.0, < 2.12.6"],"patched":["nats-server 2.12.6"],"published":"2026-03-25","updated":"2026-09-09","sourceUpdated":"2026-09-09T13:19:24.173","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-33219","references":[{"url":"https://advisories.nats.io/CVE/secnote-2026-02.txt","label":"security-advisories@github.com"},{"url":"https://advisories.nats.io/CVE/secnote-2026-11.txt","label":"security-advisories@github.com"},{"url":"https://github.com/advisories/GHSA-qrvq-68c2-7grw","label":"security-advisories@github.com"},{"url":"https://github.com/nats-io/nats-server/security/advisories/GHSA-8r68-gvr4-jh7j","label":"security-advisories@github.com"},{"url":"https://access.redhat.com/errata/RHSA-2026:21769","label":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c"},{"url":"https://access.redhat.com/errata/RHSA-2026:22347","label":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c"},{"url":"https://access.redhat.com/errata/RHSA-2026:23345","label":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c"},{"url":"https://access.redhat.com/security/cve/CVE-2026-33219","label":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2451445","label":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33219.json","label":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-33219"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-33219"}],"tags":["nvd","cve.org","csaf","vex","red-hat","score-dispute"],"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"partial","timestamp":"2026-03-25T20:10:18.603979Z"},"epss":0.00525,"epssPercentile":0.43317,"scores":{"nvd":5.3,"vendor":7.5,"cna":5.3},"ingestedAt":"2026-07-20T12:38:40.736Z","slug":"CVE-2026-33219","body":"## Overview\n\nNATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions 2.11.15 and 2.12.6, a 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. This is a milder variant of CVE-2026-27571. That earlier issue was a compression bomb, this vulnerability is not. Attacks against this new issue thus require significant client bandwidth. Versions 2.11.15 and 2.12.6 contain a fix. As a workaround, disable websockets if not required for project deployment.\n\n## Affected\n\n- `nats-server < 2.11.15`\n- `nats-server >= 2.12.0, < 2.12.6`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `nats-server 2.12.6`\n\n## Vendor advisories\n\n- **RHSA-2026:22347** · Red Hat · fixed in: Multicluster Global Hub 1.4.5 · released 2026-06-01 · [advisory](https://access.redhat.com/errata/RHSA-2026:22347)\n- **RHSA-2026:23345** · Red Hat · fixed in: Multicluster Global Hub 1.6.5 · released 2026-06-04 · [advisory](https://access.redhat.com/errata/RHSA-2026:23345)\n- **RHSA-2026:21769** · Red Hat · fixed in: Red Hat multicluster global hub 1.5.3 · released 2026-05-28 · [advisory](https://access.redhat.com/errata/RHSA-2026:21769)","depth":"sunlit","depthScore":29,"depthScoreParts":{"impact":29.2,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}