NATS has pre-auth server panic via leafnode handling

High7.5CVE-2026-33218 · Published Mar 24, 2026 · updated Sep 10, 2026

### Background NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing. The nats-server allows hub/spoke topologies using "leafnode" connections by other nats-servers. ### Problem Description A client which can connect to the leafnode port can crash the nats-server with a certain malformed message pre-authentication. ### Affected Versions Any version before v2.12.6 or v2.11.15 ### Workarounds 1. Disable leafnode support if not needed. 2. Restrict network connections to your leafnode port, if plausible without compromising the service offered. ### References * This document is canonically: <https://advisories.nats.io/CVE/secnote-2026-10.txt> * GHSA advisory: <https://github.com/nats-io/nats-server/security/advisories/GHSA-vprv-35vv-q339> * MITRE CVE entry: <https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-33218>