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Nats ServerApplication · Linuxfoundation

CVE-2026-33218

HIGH · 7.5 CVSS v3.1 Published 2026-03-25
Fix available
A fix is available. Upgrade to 2.11.15 / 2.12.6 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions 2.11.15 and 2.12.6, a client which can connect to the leafnode port can crash the nats-server with a certain malformed message pre-authentication. Versions 2.11.15 and 2.12.6 contain a fix. As a workaround, disable leafnode support if not needed or restrict network connections to the leafnode port, if plausible without compromising the service offered.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A denial-of-service vulnerability in NATS-Server versions prior to 2.11.15 and 2.12.6 allows an unauthenticated client connecting to the leafnode port to crash the server by sending a specifically malformed message before authentication completes.

MitigationUpgrade to NATS-Server version 2.11.15 or 2.12.6, or as a workaround disable leafnode support if not needed or restrict network access to the leafnode port.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Nats ServerApplication
Affected:< 2.11.15>= 2.12.0, < 2.12.6

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify if NATS Server is running
    Run 'ps aux | grep nats-server' or check running services to see if the NATS Server process is active
    Affected if NATS Server is running and exposed on a network
  2. Determine the installed NATS Server version
    Run 'nats-server --version' or check the version via 'nats-server -v' command
    Affected if Version is less than 2.11.15, or between 2.12.0 and 2.12.5 inclusive
  3. Check if leafnode support is enabled
    Review the NATS Server configuration file (typically nats.conf) for 'leaf' or 'leafnode' directives, or run 'nats-server --help' to see if leafnode module is compiled in
    Affected if Leafnode support is enabled in the configuration
  4. Identify the leafnode port exposure
    Check the configuration file for 'leafnodes' block with 'listen' directive, or inspect netstat/ss output for ports in the 7000-9000 range that NATS is bound to
    Affected if Leafnode port is accessible from network (not localhost-only or firewalled)
  5. Verify authentication status on leafnode port
    Review the configuration for leafnode-specific authentication settings; check if 'authorization' or 'auth' block applies to leafnode connections before authentication
    Affected if Leafnode connections can be established before authentication completes

You are affected if NATS Server version is below 2.11.15 or between 2.12.0-2.12.5 AND leafnode port is network-accessible with no pre-authentication protection.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 2.11.15 / 2.12.6 or later
Fixed in 2.11.152.12.6
Interim mitigation

Upgrade to NATS-Server version 2.11.15 or 2.12.6, or as a workaround disable leafnode support if not needed or restrict network access to the leafnode port.

Recommended fix High confidence

NATS Server 2.11.15 or 2.12.6 (or latest stable release)

  1. Identify current NATS Server version by running 'nats-server --version' or checking the server logs
  2. Upgrade to NATS Server version 2.11.15 or 2.12.6 (or the latest stable release in that branch)
  3. For package managers: use 'go install github.com/nats-io/nats-server/v2@latest' or download the appropriate binary from the NATS releases page
  4. Restart the NATS Server after upgrade
  5. Verify the server starts successfully and is not crashing on malformed leafnode messages
  6. Alternatively, if upgrade is not immediately feasible, disable leafnode support in nats-server.conf by removing or commenting out 'leaf {}' blocks, or restrict network access to the leafnode port (default 7422) using firewall rules

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Nats Server Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,240
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,984.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-33218 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data