NATS has pre-auth server panic via leafnode handling

CVE-2026-33218 → View on GitHub ↗ View on CVE.org ↗ View on NVD ↗

Description

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.

Problem Description

A client which can connect to the leafnode port can crash the nats-server with a certain malformed message pre-authentication.

Affected Versions

Any version before v2.12.6 or v2.11.15

Workarounds

  1. Disable leafnode support if not needed.
  2. Restrict network connections to your leafnode port, if plausible without compromising the service offered.

References

  • This document is canonically: <https://advisories.nats.io/CVE/secnote-2026-10.txt>
  • GHSA advisory: <https://github.com/nats-io/nats-server/security/advisories/GHSA-vprv-35vv-q339>
  • MITRE CVE entry: <https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-33218>

Basic information

Type
reviewed
Severity
high
Advisory on GitHub
Open advisory ↗
Repository advisory
Open repository advisory ↗
Source code
Browse source ↗
Published (advisory)
2026-03-24 21:45:29 UTC
Updated
2026-03-27 22:09:49 UTC
GitHub reviewed
2026-03-24 21:45:29 UTC
NVD published
2026-03-25

EPSS Score

Score Percentile
0.17% 37.58%

CVSS Scores

Base score Version Severity Vector
7.5 3.1 —
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.

Identifiers

Type Value
GHSA GHSA-vprv-35vv-q339 ↗
CVE CVE-2026-33218 ↗

CWEs

CWE id Name
CWE-20 Improper Input Validation

Affected packages (3)

Vulnerable version ranges and first patched releases as published by GitHub.

Ecosystem Package Vulnerable range First patched Vulnerable functions
go github.com/nats-io/nats-server/v2 < 2.11.15 2.11.15 —
go github.com/nats-io/nats-server/v2 >= 2.12.0-RC.1, < 2.12.6 2.12.6 —
go github.com/nats-io/nats-server > 0 — —

References

cvelogic Threat Intelligence