NATS is vulnerable to pre-auth DoS through WebSockets client service
Description
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.
Affected packages
Versions sourced from the GitHub Security Advisory.
| Package | Affected versions | Patched versions |
|---|---|---|
github.com/nats-io/nats-server/v2Go | < 2.11.15 | 2.11.15 |
github.com/nats-io/nats-server/v2Go | >= 2.12.0-RC.1, < 2.12.6 | 2.12.6 |
github.com/nats-io/nats-serverGo | >= 0 | — |
Affected products
1- Range: < 2.11.15
Patches
0No patches discovered yet.
Vulnerability mechanics
AI mechanics synthesis has not run for this CVE yet.
References
6- github.com/advisories/GHSA-8r68-gvr4-jh7jghsaADVISORY
- github.com/advisories/GHSA-qrvq-68c2-7grwghsax_refsource_MISCADVISORY
- nvd.nist.gov/vuln/detail/CVE-2026-33219ghsaADVISORY
- advisories.nats.io/CVE/secnote-2026-02.txtghsax_refsource_MISCWEB
- advisories.nats.io/CVE/secnote-2026-11.txtghsax_refsource_MISCWEB
- github.com/nats-io/nats-server/security/advisories/GHSA-8r68-gvr4-jh7jghsax_refsource_CONFIRMWEB
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