NATS is vulnerable to pre-auth DoS through WebSockets client service
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-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.
describes (1)
Related CVEs.
| ID | severity | exploitable | ||
|---|---|---|---|---|
| CVE-2026-33219US | — | — | ||
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 We… | ||||
references
External citations — patches, advisories, analysis.
- https://access.redhat.com/errata/RHSA-2026:21769WEB
- https://access.redhat.com/errata/RHSA-2026:22347WEB
- https://access.redhat.com/errata/RHSA-2026:23345WEB
- https://access.redhat.com/security/cve/CVE-2026-33219WEB
- https://advisories.nats.io/CVE/secnote-2026-02.txtADVISORY
- https://advisories.nats.io/CVE/secnote-2026-11.txtADVISORY
- https://bugzilla.redhat.com/show_bug.cgi?id=2451445WEB
- https://github.com/advisories/GHSA-qrvq-68c2-7grwADVISORY
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