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

Source: https://junglewise.ai/threats/cve-2026-33218-nats-server-denial-of-service-in-leafnode-handling  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-03-25. Updated: 2026-06-30  
License: CC BY 4.0 with a link back

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)](https://junglewise.ai/threats/technologies/github-com-nats-io-nats-server), [github.com/nats-io/nats-server/v2 (Go)](https://junglewise.ai/threats/technologies/github-com-nats-io-nats-server-v2), [Red Hat Multicluster Global Hub](https://junglewise.ai/threats/technologies/multicluster-global-hub). Vendors: [Go](https://junglewise.ai/threats/vendors/go), [Red Hat](https://junglewise.ai/threats/vendors/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

  ```sh
  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

- [https://advisories.nats.io/CVE/secnote-2026-10.txt](https://advisories.nats.io/CVE/secnote-2026-10.txt)
- [https://github.com/nats-io/nats-server/security/advisories/GHSA-vprv-35vv-q339](https://github.com/nats-io/nats-server/security/advisories/GHSA-vprv-35vv-q339)
- [https://access.redhat.com/errata/RHSA-2026:21769](https://access.redhat.com/errata/RHSA-2026:21769)
- [https://access.redhat.com/errata/RHSA-2026:22347](https://access.redhat.com/errata/RHSA-2026:22347)
- [https://access.redhat.com/errata/RHSA-2026:23345](https://access.redhat.com/errata/RHSA-2026:23345)
- [https://access.redhat.com/security/cve/CVE-2026-33218](https://access.redhat.com/security/cve/CVE-2026-33218)
- [https://bugzilla.redhat.com/show_bug.cgi?id=2451450](https://bugzilla.redhat.com/show_bug.cgi?id=2451450)

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