CVE-2026-33246

Background

NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing.

The nats-server allows hub/spoke topologies using "leafnode" connections by other nats-servers. NATS messages can have headers.

Problem Description

The nats-server offers a Nats-Request-Info: message header, providing information about a request. This is supposed to provide enough information to allow for account/user identification, such that NATS clients could make their own decisions on how to trust a message, provided that they trust the nats-server as a broker.

A leafnode connecting to a nats-server is not fully trusted unless the system account is bridged too. Thus identity claims should not have propagated unchecked.

Thus NATS clients relying upon the Nats-Request-Info: header could be spoofed.

Does not directly affect the nats-server itself, but the CVSS Confidentiality and Integrity scores are based upon what a hypothetical client might choose to do with this NATS header.

Affected Versions

Any version before v2.12.6 or v2.11.15

Workarounds

None.

The application does not adequately verify the identity of a user, device, or process before granting access. Typical impact: unauthorized access to functions or data reserved for authenticated parties.

CVE-2026-33246 has a CVSS score of 6.4 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.11.15, 2.12.6); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-33246? CVE-2026-33246 is a medium-severity improper authentication vulnerability in github.com/nats-io/nats-server/v2 (go), affecting versions < 2.11.15. It is fixed in 2.11.15, 2.12.6. The application does not adequately verify the identity of a user, device, or process before granting access.
2. How severe is CVE-2026-33246? CVE-2026-33246 has a CVSS score of 6.4 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by CVE-2026-33246?
   • github.com/nats-io/nats-server/v2 (go) (versions < 2.11.15)
   • github.com/nats-io/nats-server (go) (versions > 0)
4. Is there a fix for CVE-2026-33246? Yes. CVE-2026-33246 is fixed in 2.11.15, 2.12.6. Upgrade to this version or later.
5. Is CVE-2026-33246 exploitable, and should I be worried? Whether CVE-2026-33246 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-33246 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-33246?
   • Upgrade github.com/nats-io/nats-server/v2 to 2.11.15 or later
   • Upgrade github.com/nats-io/nats-server/v2 to 2.12.6 or later