CVE-2026-27889: Linuxfoundation Nats-Server

High severity, CVSS 7.5. EPSS: 0.8% 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. Starting in version 2.2.0 and prior to versions 2.11.14 and 2.12.5, a missing sanity check on a WebSockets frame could trigger a server panic in the nats-server. This happens before authentication, and so is exposed to anyone who can connect to the websockets port. Versions 2.11.14 and 2.12.5 contains a fix. A workaround is available. The vulnerability only affects deployments which use WebSockets and which expose the network port to untrusted end-points. If one is able to do so, a defense in depth of restricting either of these will mitigate the attack.

Affected products

• Linuxfoundation Nats-Server: from 2.2.0, before 2.11.14 (fixed in 2.11.14); from 2.12.0, before 2.12.5 (fixed in 2.12.5)

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