CVE-2026-33219

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.

How to fix CVE-2026-33219

To remediate CVE-2026-33219, upgrade the affected package to a fixed version below.

• —upgrade to 2.11.15 or later
• —no fix listed
• —no fix listed
• —no fix listed
• —upgrade to 2.11.15 or later
• —upgrade to 2.11.15 or later

Is CVE-2026-33219 being exploited?

Low — EPSS is 0.1%, meaning exploitation activity has not been observed at scale.

Affected packages (6)

• from 0, < 2.11.15, >= 2.12.0, < 2.12.6
• from 0
• from 0
• from 0
• from 0, < 2.11.15
• from 0, < 2.11.15, >= 2.12.0-RC.1, < 2.12.6

CVSS scores

References (7)

• ADVISORYgithub.com/advisories/GHSA-qrvq-68c2-7grw
• ADVISORYnvd.nist.gov/vuln/detail/CVE-2026-33219
• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2026-33219
• PATCHgithub.com/nats-io/nats-server
• WEB