CVE-2026-58211: nats-server Auth Bypass — Fix

Description

NATS Server is a high-performance server for NATS.io, the cloud and edge native messaging system. Prior to 2.14.3 and 2.12.12, a client could be registered as the configured no_auth_user through a parser path used when the first client operation was not CONNECT, bypassing user-level connection restrictions such as allowed_connection_types or proxy_required that normal authentication would apply. This issue is fixed in versions 2.14.3 and 2.12.12.

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CVSS v3.1 Score

5.4

MEDIUM

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

EPSS — Exploit Prediction

0.0029

Probability of exploitation

0.21%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-863 Incorrect Authorization

Affected Products

Vendor	Product	Versions
linuxfoundation	nats-server	2.12.0 — 2.12.12
linuxfoundation	nats-server	2.14.0 — 2.14.3

References

Advisories & Patches

https://github.com/nats-io/nats-server/security/advisories/GHSA-hmmp-q8cx-v964

Frequently Asked Questions

What is CVE-2026-58211? +

NATS Server is a high-performance server for NATS.io, the cloud and edge native messaging system. Prior to 2.14.3 and 2.12.12, a client could be registered as the configured no_auth_user through a parser path used when the first client operation was not CONNECT, bypassing user-level connection restrictions such as allowed_connection_types or proxy_required that normal authentication would apply. This issue is fixed in versions 2.14.3 and 2.12.12. It has a CVSS v3.1 base score of 5.4 (MEDIUM).

How severe is CVE-2026-58211? +

CVE-2026-58211 has a CVSS v3.1 score of 5.4 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0029, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-58211? +

CVE-2026-58211 affects products from linuxfoundation, specifically: nats-server. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-58211? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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