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Vulnerability · Published Mar 25, 2026 · Assigned by GitHub_M

CVE-2026-33219NATS is vulnerable to pre-auth DoS through WebSockets client service

Medium 5.3

In plain English

A medium-severity resource allocation without limits in nats-server from nats-io. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 46% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.3Medium
Exploit odds (30 days)0.5%top 54.0% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official 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 & fixed versions

EcosystemPackageFixed inAdvisory
Alpine:v3.23nats-server2.12.6-r0ALPINE-CVE-2026-33219
Alpine:v3.24nats-server2.12.6-r0ALPINE-CVE-2026-33219
Debian:12nats-serverno fix listedDEBIAN-CVE-2026-33219
Debian:13nats-serverno fix listedDEBIAN-CVE-2026-33219
Debian:14nats-server2.12.6-1DEBIAN-CVE-2026-33219
Gogithub.com/nats-io/nats-serverno fix listedGHSA-8r68-gvr4-jh7j
Gogithub.com/nats-io/nats-serverno fix listedGO-2026-4831
Gogithub.com/nats-io/nats-server/v22.11.15, 2.12.6GO-2026-4831
Gogithub.com/nats-io/nats-server/v22.11.15GHSA-8r68-gvr4-jh7j
Gogithub.com/nats-io/nats-server/v22.12.6GHSA-8r68-gvr4-jh7j
Ubuntu:24.04:LTSnats-serverno fix listedUBUNTU-CVE-2026-33219
Ubuntu:25.10nats-serverno fix listedUBUNTU-CVE-2026-33219
Ubuntu:26.10nats-serverno fix listedUBUNTU-CVE-2026-33219

Affected products (as reported)

VendorProductVersions
nats-io nats-server < 2.11.15>= 2.12.0-RC.1, < 2.12.6

Weakness: CWE-770 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

References