CVE-2026-33246Network attack vector

Identity spoofing via unchecked leafnode header propagation

Published Mar 25, 2026 · Updated Mar 25, 2026

Authentication bypass in NATS Server before 2.11.15 and 2.12.0-RC.1 through 2.12.5 allows remote authenticated users to spoof identities. The server propagates Nats-Request-Info identity claims from a leafnode without validating them when the system account is not bridged. Exploitation requires a leafnode connection and a downstream client that trusts the header; resulting data access or actions depend on that client's authorization decisions.

CVSS severity6.4
Medium
EPSS probability0.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in NATS Server before 2.11.15 and 2.12.0-RC.1 through 2.12.5 allows remote authenticated users to spoof identities. The server propagates Nats-Request-Info identity claims from a leafnode without validating them when the system account is not bridged. Exploitation requires a leafnode connection and a downstream client that trusts the header; resulting data access or actions depend on that client's authorization decisions.

The record

CVE
CVE-2026-33246
Published
Mar 25, 2026
Updated
Mar 25, 2026
Vendor
NATS.io
Product
NATS Server
Classifications
CWE-290, CWE-287, T1565.002
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 25, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 25, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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

  1. Affected versionversion=< 2.11.15
  2. Affected versionversion=>= 2.12.0-RC.1, < 2.12.6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

NATS.io · NATS Serverversion=< 2.11.15; version=>= 2.12.0-RC.1, < 2.12.6

Published CVSS scores

5.4NISTCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
6.4GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N

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)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-290Authentication Bypass by Spoofing
CWE-287Improper Authentication
T1565.002Transmitted Data Manipulation

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

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Your stack

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