CVE-2026-33218: NATS-Server denial of service in leafnode handling

CVE-2026-33218 · Severity: high · CVSS 7.5 · Published 2026-03-25

NATS-Server is a high-performance messaging system used for cloud and edge computing to facilitate communication between different applications. A vulnerability exists where an unauthenticated attacker can send a specially crafted message to the server's leafnode port, causing the service to crash. This results in a denial-of-service (DoS) condition, disrupting communication across the network and potentially halting business operations that rely on the messaging system.

Technologies: github.com/nats-io/nats-server (Go), github.com/nats-io/nats-server/v2 (Go), Red Hat Multicluster Global Hub. Vendors: Go, Red Hat.

Quick answers

Is CVE-2026-33218 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-33218 being exploited in the wild.
How severe is CVE-2026-33218?
High severity, with a CVSS score of 7.5, published 25 March 2026.
Which products and versions are affected?
github.com/nats-io/nats-server (Go) SEMVER:introduced=0; github.com/nats-io/nats-server/v2 (Go) SEMVER:introduced=0,fixed=2.11.15, SEMVER:introduced=0,fixed=2.11.15,introduced=2.12.0-RC.1,fixed=2.12.6.
Is there a fix for CVE-2026-33218?
Yes. github.com/nats-io/nats-server/v2 (Go): upgrade to 2.11.15, 2.12.6 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-33218 attacked?
It is attacked over the network, in a hosted service.
Am I affected by CVE-2026-33218?
Check whether you run github.com/nats-io/nats-server (Go), github.com/nats-io/nats-server/v2 (Go) or Red Hat Multicluster Global Hub at an affected version. 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.

How to fix

  • github.com/nats-io/nats-server/v2 (Go): upgrade to 2.11.15, 2.12.6 or later
    go get github.com/nats-io/nats-server/v2@v2.12.6

Technical details

A denial-of-service vulnerability exists in NATS-Server due to improper input validation (CWE-20) or improper validation of syntactic correctness (CWE-1286) within the leafnode handling component. An unauthenticated remote attacker with network access to the leafnode port can trigger a server panic by sending a malformed message. This exploit occurs pre-authentication, meaning no valid credentials are required to crash the service. The vulnerability affects all versions prior to 2.11.15 and 2.12.6. Patches are available in versions 2.11.15 and 2.12.6; workarounds include disabling leafnode support or implementing network-level access controls on the leafnode port.

Affected products

  • nats-io nats-server < 2.11.15, >= 2.12.0-RC.1 < 2.12.6
  • Red Hat Multicluster Global Hub 1.4.5
  • Red Hat Multicluster Global Hub 1.5.4
  • Red Hat Multicluster Global Hub 1.6.2

Identifiers

  • CVE-2026-33218
  • GHSA-vprv-35vv-q339
  • GO-2026-4837

Timeline

  • 2026-03-24: advisory: NATS project released security advisory 2026-10
  • 2026-03-25: disclosed: CVE-2026-33218 published
  • 2026-05-28: patched: Red Hat released security update RHSA-2026:21769 for Multicluster Global Hub

References

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