CVE-2026-33219 MEDIUM

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

Vendor Nats-Io
Product nats-server
Weakness CWE-770 · Uncontrolled resource consumption
Published March 25, 2026
Last update June 30, 2026
View on NVD All CVEs

CVSS base score

5.3/10
Attack vector Network
Attack complexity Low
Privileges required None
User interaction None
Confidentiality None
Integrity None

CVSS vector

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

What the vulnerability does

01Description

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.

Key dates

02Disclosure timeline

March 25, 2026 CVE published
June 30, 2026 Record updated