CVE-2026-27889

HIGH 7.5

NATS: Pre-auth remote server crash via WebSocket frame length overflow in wsRead

CVSS Score

7.5

EPSS Score

0.0%

EPSS Percentile

0th

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.

CWE	CWE-190
Vendor	nats-io
Product	nats-server
Published	Mar 25, 2026
Last Updated	Mar 25, 2026

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CVSS v3 Breakdown

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Affected Versions

nats-io / nats-server

>= 2.2.0, < 2.11.14 >= 2.12.0, < 2.12.5

References

NVD ↗ CVE.org ↗ EPSS Data ↗

github.com: https://github.com/nats-io/nats-server/security/advisories/GHSA-pq2q-rcw4-3hr6 advisories.nats.io: https://advisories.nats.io/CVE/secnote-2026-03.txt