NATS is vulnerable to pre-auth DoS through WebSockets client service
### Background NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing. The nats-server offers a WebSockets client service, used in deployments where browsers are the NATS clients. ### Problem Description 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 [NATS-advisory-ID 2026-02](https://advisories.nats.io/CVE/secnote-2026-02.txt) (aka CVE-2026-27571; GHSA-qrvq-68c2-7grw). That earlier issue was a compression bomb, this vulnerability is not. Attacks against this new issue thus require significant client bandwidth. ### Affected Versions Any version before v2.12.6 or v2.11.15 ### Workarounds 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://advisories.nats.io/CVE/secnote-2026-02.txtWEB
- https://advisories.nats.io/CVE/secnote-2026-11.txtWEB
- https://github.com/advisories/GHSA-qrvq-68c2-7grwADVISORY
- https://github.com/nats-io/nats-serverPACKAGE
- https://github.com/nats-io/nats-server/security/advisories/GHSA-8r68-gvr4-jh7jWEB
- https://nvd.nist.gov/vuln/detail/CVE-2026-33219ADVISORY
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