CVE-2026-33219

MEDIUM 5.3

NATS is vulnerable to pre-auth DoS through WebSockets client service

CVSS Score

5.3

EPSS Score

0.0%

EPSS Percentile

0th

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.

CWE	CWE-770
Vendor	nats-io
Product	nats-server
Published	Mar 25, 2026
Last Updated	Mar 25, 2026

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CVSS v3 Breakdown

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

Low

Affected Versions

nats-io / nats-server

< 2.11.15 >= 2.12.0-RC.1, < 2.12.6

References

NVD ↗ CVE.org ↗ EPSS Data ↗

github.com: https://github.com/nats-io/nats-server/security/advisories/GHSA-8r68-gvr4-jh7j advisories.nats.io: https://advisories.nats.io/CVE/secnote-2026-02.txt advisories.nats.io: https://advisories.nats.io/CVE/secnote-2026-11.txt github.com: https://github.com/advisories/GHSA-qrvq-68c2-7grw