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Nats ServerApplication · Linuxfoundation

CVE-2026-33217

MEDIUM · 6.5 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 →
74/100
Remediation priority · Elevated
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, when using ACLs on message subjects, these ACLs were not applied in the `$MQTT.>` namespace, allowing MQTT clients to bypass ACL checks for MQTT subjects. Versions 2.11.15 and 2.12.6 contain a fix. No known workarounds are available.

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

In NATS-Server versions prior to 2.11.15 and 2.12.6, Access Control Lists (ACLs) configured for message subjects were not enforced within the `$MQTT.>` namespace, allowing MQTT clients to bypass ACL checks for MQTT-related subjects.

MitigationUpgrade NATS-Server to version 2.11.15 or 2.12.6 to apply ACLs correctly in the `$MQTT.>` namespace.

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
Low
Integrity
Low
Availability
None

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

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. Check installed NATS-Server version
    Run 'nats-server --version' or check the binary version. On Linux, you can also use 'nats-server -v' or check the package version with your package manager (e.g., 'dpkg -l nats-server' or 'rpm -qi nats-server').
    Affected if The installed version is less than 2.11.15, or is 2.12.0 through 2.12.5 (inclusive)
  2. Verify MQTT protocol support is enabled
    Inspect the NATS-Server configuration file (typically nats.conf) for 'mqtt { }' block or check if the server is listening on MQTT ports (default 1883 for TCP or 4222 for MQTT over websocket). You can also check running processes for MQTT flags or use 'nats-server --help' to see enabled protocols.
    Affected if MQTT support is enabled and the server is accepting MQTT connections
  3. Identify ACL rules for message subjects
    Review the NATS-Server configuration file for 'acl' or 'authorization' blocks. Look for 'publish' or 'subscribe' permissions defined with subject patterns. Specifically search for any rules that reference '>' (wildcard) or patterns that could match the '$MQTT.>' namespace.
    Affected if ACL rules are defined that restrict access to subjects, particularly any subjects that would overlap with the '$MQTT.>' namespace
  4. Check if ACL rules apply to $MQTT.> namespace
    Examine the ACL configuration for any rules with subjects like '$MQTT.>', '$MQTT.msg.*', '$MQTT.sub.*', or broader patterns that include the '$MQTT.' prefix. Use 'nats reporter account' or check the resolved ACLs via the monitoring port if available.
    Affected if ACL rules exist that govern access to subjects within the '$MQTT.>' namespace (these rules would be bypassed in vulnerable versions)

A user is affected if they run a vulnerable NATS-Server version (before 2.11.15 or 2.12.0-2.12.5) with MQTT enabled and have configured ACL rules that restrict access to the '$MQTT.>' namespace.

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 NATS-Server to version 2.11.15 or 2.12.6 to apply ACLs correctly in the `$MQTT.>` namespace.

Recommended fix High confidence

Upgrade to NATS Server 2.11.15 (if on 2.11.x line) or 2.12.6 (if on 2.12.x line)

  1. Identify current NATS Server version by checking the server logs or running `nats-server --version`
  2. Stop the NATS Server gracefully to avoid disrupting active connections
  3. Back up the NATS Server configuration files, persistence data, and any custom scripts
  4. Upgrade NATS Server to version 2.11.15 or 2.12.6 (choose the version appropriate for your release line)
  5. Verify the integrity of the downloaded package using checksums if provided
  6. Start the upgraded NATS Server
  7. Confirm the server starts successfully and logs indicate the new version
  8. Test MQTT client connections and verify ACLs are now properly enforced in the `$MQTT.>` namespace
Caveat Review release notes for any deprecation notices or configuration changes between your current version and the target version before upgrading

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
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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-2026-33217 in production — separate from our analysis above.

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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