CVE-2026-29785

NATS Server panic via malicious compression on leafnode port in github.com/nats-io/nats-server

### Background NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing. When configured to accept leafnode connections (for a hub/spoke topology of multiple nats-servers), then the default configuration allows for negotiating compression; a malicious remote NATS server can trigger a server panic via that compression. ### Problem Description If the nats-server has the "leafnode" configuration enabled (not default), then anyone who can connect can crash the nats-server by triggering a panic. This happens pre-authentication and requires that compression be enabled (which it is, by default, when leafnodes are used). Context: a NATS server can form various clustering topologies, including local clusters, and superclusters of clusters, but leafnodes allow for separate administrative domains to link together with limited data communication; eg, a server in a moving vehicle might use a local leafnode for agents to connect to, and sync up to a central service as and when available. The leafnode configuration here is where the central server allows other NATS servers to connect into it, almost like regular NATS clients. Documentation examples typically use port 7422 for leafnode communications. ### Affected Versions Version 2, prior to v2.11.14 or v2.12.5 ### Workarounds Disable compression on the leafnode port: ``` leafnodes { port: 7422 compression: off } ```

NATS-Server es un servidor de alto rendimiento para NATS.io, un sistema de mensajería nativo de la nube y del borde. Antes de las versiones 2.11.14 y 2.12.5, si el nats-server tiene la configuración 'leafnode' habilitada (no predeterminada), entonces cualquiera que pueda conectarse puede bloquear el nats-server al desencadenar un pánico. Esto ocurre antes de la autenticación y requiere que la compresión esté habilitada (lo cual está habilitado, por defecto, cuando se usan leafnodes). Las versiones 2.11.14 y 2.12.5 contienen una corrección. Como solución alternativa, deshabilite la compresión en el puerto leafnode.