CVE-2026-58253

Unauthenticated inter-server access via parser fast path

Published Jul 8, 2026 · Updated Jul 8, 2026

Authentication bypass in NATS Server before 2.11.16 and 2.12.0-preview.1 through 2.12.6 grants remote attackers inter-server access. The server/parser.go parser applies the no_auth_user pre-CONNECT fast path to route and leafnode sockets instead of limiting it to client connections. Network access to either listener and the non-default no_auth_user setting are required; exploitation permits message injection and privileged inter-server operations.

CVSS severity8.8
High
EPSS probability0.37%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Authentication bypass in NATS Server before 2.11.16 and 2.12.0-preview.1 through 2.12.6 grants remote attackers inter-server access. The server/parser.go parser applies the no_auth_user pre-CONNECT fast path to route and leafnode sockets instead of limiting it to client connections. Network access to either listener and the non-default no_auth_user setting are required; exploitation permits message injection and privileged inter-server operations.

The record

CVE
CVE-2026-58253
Published
Jul 8, 2026
Updated
Jul 8, 2026
Vendor
NATS.io
Product
NATS Server
Classifications
CWE-287, T1190
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 8, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 8, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 2.11.16
  2. Affected versionversion=>= 2.12.0-preview.1, < 2.12.6

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

NATS.io · NATS Serverversion=< 2.11.16; version=>= 2.12.0-preview.1, < 2.12.6

Published CVSS scores

8.8GitHubCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-287Improper Authentication
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo