Authentication Bypass in NATS Server

Publication date: 2026-07-08

Last updated on: 2026-07-08

Assigner: GitHub, Inc.

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.

CVSS Scores

EPSS Scores

Probability:
Percentile:

Meta Information

Published

2026-07-08

Last Modified

2026-07-08

Generated

2026-07-09

AI Q&A

2026-07-09

EPSS Evaluated

N/A

NVD

CVE-2026-58211

Affected Vendors & Products

Vendor	Product	Version / Range
nats_io	nats_server	to 2.14.3 (inc)
nats_io	nats_server	to 2.12.12 (inc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-863	The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.

Attack-Flow Graph

Executive Summary

This vulnerability affects the NATS Server, a high-performance messaging server. Before versions 2.14.3 and 2.12.12, a client could be mistakenly registered as the configured no_auth_user by exploiting a parser path triggered when the first client operation was not a CONNECT command. This bypass allowed the client to circumvent user-level connection restrictions such as allowed_connection_types or proxy_required, which normally enforce authentication and connection policies.

Impact Analysis

The vulnerability can lead to unauthorized clients bypassing authentication and connection restrictions. This means an attacker could connect to the NATS Server without proper credentials or restrictions, potentially gaining limited access to the messaging system. The impact includes partial confidentiality and integrity loss, as indicated by the CVSS score, but no impact on availability.

Mitigation Strategies

To mitigate this vulnerability, you should upgrade your NATS Server to version 2.14.3 or 2.12.12 or later, where the issue is fixed.

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