# CVE-2026-27889: nats-server: NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system

CVE-2026-27889 is fixed in 2 products on 1 platform, first by DEBIAN-CVE-2026-27889, released March 25, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-27889
- Priority: High
- CVSS: 7.5 (high)
- EPSS: 0.0059
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Mar 25, 2026

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | govulncheck-vulndb opensuse-leap 15.6 | 0.0.20260326T203309-150000.1.155.2 | [SUSE-SU-2026:1135-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-1135-1.md) | Mar 27, 2026 |
| Linux | govulncheck-vulndb opensuse-leap 16.0 | 0.0.20260723T184607-160000.1.1 | [OPENSUSE-SU-2026:21483-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21483-1.md) | Jul 30, 2026 |
| Linux | nats-server Debian 14 | 2.12.6-1 | [DEBIAN-CVE-2026-27889](https://patchblox.com/security/data/fix/linux/debian-cve-2026-27889.md) | Mar 25, 2026 |

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Data as of 2026-11-08T13:06:02Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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