Is CVE-2026-58253 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-58253 being exploited in the wild.

How severe is CVE-2026-58253?

High severity, with a CVSS score of 8.8, published 8 July 2026.

Which products and versions are affected?

NATS.io NATS Server = 2.12.0-preview.1, < 2.12.7, < 2.14.0.

Is there a fix for CVE-2026-58253?

A patch was published on 2026-07-08. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-58253 attacked?

It is attacked from the adjacent network, in a hosted service.

Am I affected by CVE-2026-58253?

Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-58253: NATS Server authentication bypass in route or leafnode listeners

Q: Is there a fix for CVE-2026-58253?

A patch was published on 2026-07-08. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

Q: How is CVE-2026-58253 attacked?

It is attacked from the adjacent network, in a hosted service.

Q: Am I affected by CVE-2026-58253?

Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-58253 · Severity: high · CVSS 8.8 · Published 2026-07-08

NATS Server is a messaging system used to connect cloud and edge applications. A security flaw allows unauthorized users to bypass authentication when the server is configured to allow certain guest access. This could allow an attacker to impersonate a trusted server or node, potentially leading to unauthorized data access or disruption of the messaging network.

Quick answers

Is CVE-2026-58253 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-58253 being exploited in the wild.
How severe is CVE-2026-58253?: High severity, with a CVSS score of 8.8, published 8 July 2026.
Which products and versions are affected?: NATS.io NATS Server < 2.11.16, >= 2.12.0-preview.1, < 2.12.7, < 2.14.0.
Is there a fix for CVE-2026-58253?: A patch was published on 2026-07-08. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-58253 attacked?: It is attacked from the adjacent network, in a hosted service.
Am I affected by CVE-2026-58253?: Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

An authentication bypass vulnerability exists in NATS Server when the 'no_auth_user' option is enabled. A parser 'fast path' optimization, originally intended only for standard client connections, was incorrectly applied to route and leafnode listeners. An unauthenticated attacker on an adjacent network can exploit this to bypass inter-server CONNECT authentication. Successful exploitation allows the attacker to operate with the elevated privileges associated with server-to-server or leafnode connection types. The issue is addressed in versions 2.14.0, 2.12.7, and 2.11.16 by restricting the 'no_auth_user' logic to client connections only.

Affected products

NATS.io NATS Server < 2.11.16, >= 2.12.0-preview.1, < 2.12.7, < 2.14.0

Timeline

2026-07-08: disclosed
2026-07-08: advisory
2026-07-08: patched

References

This page as Markdown. Free to reuse under CC BY 4.0 with a link back.