CVE-2026-33219

low-risk

Published 2026-03-25

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.

Do I need to act?

0.08% chance of exploitation

EPSS score — low exploit probability

Not on CISA KEV list

No confirmed active exploitation reported to CISA

Patch status unknown

Check vendor advisories for fix availability and mitigation guidance

CVSS 5.3/10 Medium

NETWORK / LOW complexity

Affected Products (1)

Nats-Server

Affected Vendors

Linuxfoundation

References (4)

Mitigation https://advisories.nats.io/CVE/secnote-2026-02.txt

Mitigation https://advisories.nats.io/CVE/secnote-2026-11.txt

Mitigation https://github.com/advisories/GHSA-qrvq-68c2-7grw

Mitigation https://github.com/nats-io/nats-server/security/advisories/GHSA-8r68-gvr4-jh7j

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low-risk

Severity 21/34 · High

Exploitability 0/34 · Minimal

Exposure 5/34 · Minimal