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.
Problem types
CWE-770: Allocation of Resources Without Limits or Throttling
Product status
>= 2.12.0-RC.1, < 2.12.6
References
github.com/...server/security/advisories/GHSA-8r68-gvr4-jh7j
advisories.nats.io/CVE/secnote-2026-02.txt
advisories.nats.io/CVE/secnote-2026-11.txt
github.com/advisories/GHSA-qrvq-68c2-7grw