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Integer OverflowWeakness · CWE-190

CVE-2026-40046

HIGH · 7.5 CVSS v3.1 Published 2026-04-09
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
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
Integer Overflow or Wraparound vulnerability in Apache ActiveMQ, Apache ActiveMQ All, Apache ActiveMQ MQTT. The fix for "CVE-2025-66168: MQTT control packet remaining length field is not properly validated" was only applied to 5.19.2 (and future 5.19.x) releases but was missed for all 6.0.0+ versions. This issue affects Apache ActiveMQ: from 6.0.0 before 6.2.4; Apache ActiveMQ All: from 6.0.0 before 6.2.4; Apache ActiveMQ MQTT: from 6.0.0 before 6.2.4. Users are recommended to upgrade to version 6.2.4 or a 5.19.x version starting with 5.19.2 or later (currently latest is 5.19.5), which fixes the issue.

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

This is an Integer Overflow vulnerability in Apache ActiveMQ's MQTT implementation where the remaining length field in MQTT control packets is not properly validated. The issue stems from CVE-2025-66168's fix being applied only to 5.19.x versions but overlooked for 6.0.0+. A malformed remaining length field could trigger integer wraparound, potentially causing incorrect buffer allocation, heap overflow, or denial of service conditions.

MitigationUpgrade Apache ActiveMQ to version 6.2.4 or later, or to 5.19.2+ (recommended 5.19.5), to incorporate the proper validation of MQTT remaining length fields.

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

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 ActiveMQ installation and version
    Check the version file in the ActiveMQ installation directory (e.g., run `cat activemq/lib/activemq-branding-x.x.x.jar` or use `activemq --version` if available). Alternatively, check the `activemq.xml` configuration file for version indicators or the `README` file in the installation root.
    Affected if The installed version is 6.0.0 or higher, or is 5.18.x or lower (before 5.19.2)
  2. Confirm MQTT protocol support is enabled
    Inspect the ActiveMQ broker configuration file (typically `conf/activemq.xml`) for MQTT connector definitions. Look for `<transportConnector name="mqtt"` entries or similar MQTT-related transport connector configurations.
    Affected if An MQTT transport connector is defined and enabled in the broker configuration
  3. Check for unprotected MQTT listeners
    Review the transportConnector definitions in the configuration file to determine if MQTT is exposed on network-facing interfaces (check the `uri` attribute for bind addresses like `0.0.0.0` or publicly accessible IP addresses).
    Affected if MQTT connector is bound to a network-accessible interface (not localhost-only)
  4. Verify broker is running with affected version and MQTT enabled
    Cross-reference the detected version against the affected ranges (6.0.0 to 6.2.3, or versions below 5.19.2) and confirm MQTT protocol support is actively configured in the running broker.
    Affected if The broker runs a version in the affected range (6.0.0-6.2.3 or <5.19.2) AND has MQTT transport connectors configured

You are affected if your ActiveMQ broker is running version 6.0.0 through 6.2.3 or any version below 5.19.2, and has MQTT protocol support enabled in the configuration.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade Apache ActiveMQ to version 6.2.4 or later, or to 5.19.2+ (recommended 5.19.5), to incorporate the proper validation of MQTT remaining length fields.

Recommended fix High confidence

6.2.4

  1. Identify your current Apache ActiveMQ version by checking the release notes or the version file in your installation directory
  2. Stop the Apache ActiveMQ service
  3. Back up your configuration files, message data, and any custom scripts
  4. Download Apache ActiveMQ version 6.2.4 from the official Apache ActiveMQ download page (activemq.apache.org)
  5. Extract the new version to your installation directory
  6. Compare and migrate your configuration files from the backup to the new version, paying attention to any deprecation warnings
  7. Start the Apache ActiveMQ service
  8. Verify the service starts successfully and MQTT connections work properly
Caveat Review release notes between your current version and 6.2.4 for any configuration or API changes

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

Have this fixed Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,080
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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-2026-40046 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