dbcve.org
Nats ServerApplication · Linuxfoundation

CVE-2026-27889

HIGH · 7.5 CVSS v3.1 Published 2026-03-25
Fix available
A fix is available. Upgrade to 2.11.14 / 2.12.5 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. Starting in version 2.2.0 and prior to versions 2.11.14 and 2.12.5, a missing sanity check on a WebSockets frame could trigger a server panic in the nats-server. This happens before authentication, and so is exposed to anyone who can connect to the websockets port. Versions 2.11.14 and 2.12.5 contains a fix. A workaround is available. The vulnerability only affects deployments which use WebSockets and which expose the network port to untrusted end-points. If one is able to do so, a defense in depth of restricting either of these will mitigate the attack.

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 missing sanity check on WebSocket frames in NATS-Server versions 2.2.0 through versions before 2.11.14 and 2.12.5 can trigger a server panic. This occurs before authentication and is exploitable by anyone connecting to the WebSocket port.

MitigationUpdate NATS-Server to version 2.11.14 or 2.12.5. If updating is not immediately possible, mitigate by restricting network access to the WebSocket port or disabling WebSockets if not required.

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:>= 2.2.0, < 2.11.14>= 2.12.0, < 2.12.5

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. Confirm NATS-Server is running
    Run 'nats-server --version' to get the binary version, or check running process with 'ps aux | grep nats-server'
    Affected if NATS-Server process is found running on the system
  2. Identify the installed version
    Compare your installed version to the affected ranges: >= 2.2.0 and < 2.11.14, or >= 2.12.0 and < 2.12.5
    Affected if The installed version falls within any of these ranges
  3. Verify WebSocket support is enabled
    Inspect the NATS-Server configuration file (typically nats-server.conf) or run 'nats-server --help' to check for websocket enabling flags. Look for 'websocket' block or flag in the active config
    Affected if WebSocket is enabled in the configuration (vulnerability only applies when WebSocket is active)
  4. Check WebSocket port network exposure
    Review firewall rules or NATS-Server bind address settings. Use 'netstat -tlnp | grep websocket_port' or inspect the 'listen' directive in config to determine if WebSocket port is bound to an interface accessible from untrusted networks
    Affected if WebSocket port is bound to 0.0.0.0 or an IP accessible from untrusted network sources

You are affected if your NATS-Server version is between 2.2.0 and 2.11.13, or between 2.12.0 and 2.12.4, AND WebSocket is enabled and accessible from untrusted networks.

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 2.11.14 / 2.12.5 or later
Fixed in 2.11.142.12.5
Interim mitigation

Update NATS-Server to version 2.11.14 or 2.12.5. If updating is not immediately possible, mitigate by restricting network access to the WebSocket port or disabling WebSockets if not required.

Recommended fix High confidence

2.11.14 or 2.12.5 (and later)

  1. Upgrade NATS Server to version 2.11.14 or 2.12.5 (or later) to resolve the WebSockets integer overflow vulnerability
  2. If immediate upgrade is not possible, mitigate by restricting WebSocket access to trusted endpoints only, or by disabling WebSockets if not required
  3. Apply network-level access controls to limit who can reach the WebSocket port

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

Fix this in Nats Server Scoped from the published advisory
  • Consultation3.0 h
  • Implementation2.0 h
  • Testing4.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,920
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,072.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2026-27889 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2026-27889 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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