CVE-2026-27889
NATS: Pre-auth remote server crash via WebSocket frame length overflow in wsRead
Description
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.
How to fix CVE-2026-27889
To remediate CVE-2026-27889, upgrade the affected package to a fixed version below.
- —upgrade to 2.11.14 or later
- —no fix listed
- —no fix listed
- —no fix listed
- —upgrade to 2.11.14 or later
- —upgrade to 2.11.14 or later
Is CVE-2026-27889 being exploited?
Low — EPSS is 0.1%, meaning exploitation activity has not been observed at scale.
Affected packages (6)
- >= 2.2.0, < 2.11.14, >= 2.12.0, < 2.12.5
- from 0
- from 0
- from 0
- >= 2.2.0, < 2.11.14
- >= 2.2.0, < 2.11.14, >= 2.12.0, < 2.12.5
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | HIGH7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |