CVE-2026-33219: Linuxfoundation Nats-Server

Medium severity, CVSS 5.3. EPSS: 1% chance of exploitation in the next 30 days.

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 products

• Linuxfoundation Nats-Server: before 2.11.15 (fixed in 2.11.15); from 2.12.0, before 2.12.6 (fixed in 2.12.6)

Published 2026-03-25. Last modified 2026-09-09.