Auth bypass in Linuxfoundation Nats-Server

CVE-2026-58253

NATS Server is a high-performance server for NATS.io, the cloud and edge native messaging system. Prior to 2.14.0, 2.12.7, and 2.11.16, when no_auth_user was configured, a parser fast path intended for ordinary client connections could also apply to route or leafnode listeners, allowing an unauthenticated peer to bypass inter-server CONNECT authentication and operate with the privileges associated with that connection type. This issue is fixed in versions 2.14.0, 2.12.7, and 2.11.16.

Vulnerability class: Broken Authentication

Published · last modified .

CVSS v3 metric

CVSS v3 base score 8.8 (High). Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:L.

EPSS exploit prediction

EPSS: 0.004 (28.6th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 29th percentile — 28.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-58253: held from 0.004 to 0.004.

EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: 0.000

Affected products

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-58253?
CVE-2026-58253 is a high-severity vulnerability in Linuxfoundation Nats-Server, classified under Improper Authentication. CVSS score: 8.8/10. Published 2026-07-08.
How severe is CVE-2026-58253?
High severity. CVSS v3 base score is 8.8 out of 10.