ActivemqApplication · Apache
CVE-2025-66168
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 · uneditedWARNING: Users of 6.x should upgrade to 6.2.4 or later as the fix was missed in previous 6.x releases. See the following for more details: https://activemq.apache.org/security-advisories.data/CVE-2026-40046-announcement.txt https://www.cve.org/CVERecord?id=CVE-2026-40046 Original Report: Apache ActiveMQ does not properly validate the remaining length field which may lead to an overflow during the decoding of malformed packets. When this integer overflow occurs, ActiveMQ may incorrectly compute the total Remaining Length and subsequently misinterpret the payload as multiple MQTT control packets which makes the broker susceptible to unexpected behavior when interacting with non-compliant clients. This behavior violates the MQTT v3.1.1 specification, which restricts Remaining Length to a maximum of 4 bytes. The scenario occurs on established connections after the authentication process. Brokers that are not enabling mqtt transport connectors are not impacted. This issue affects Apache ActiveMQ: before 5.19.2, 6.0.0 to 6.1.8, and 6.2.0 Users are recommended to upgrade to version 5.19.2, 6.1.9, or 6.2.1, 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 confidenceApache ActiveMQ contains an integer overflow vulnerability in its MQTT protocol decoder where the Remaining Length field is not properly validated. When processing malformed MQTT packets, the overflow causes incorrect computation of the total Remaining Length, leading the broker to misinterpret payload data as multiple MQTT control packets. This occurs on established connections after authentication and only affects brokers with mqtt transport connectors enabled.
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
ActivemqApplication
< 5.19.2>= 6.0.0, <= 6.1.8= 6.2.0CVSS 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
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/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 checksWork through these to decide whether this CVE applies to you.
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Verify MQTT transport connector is enabledInspect the ActiveMQ broker configuration file (typically conf/activemq.xml) and search for <transportConnector> elements that include the 'mqtt' protocol. For example, look for lines containing <transportConnector name="mqtt" uri="mqtt://...".Affected if The broker has an mqtt transportConnector enabled. If MQTT is not configured, the vulnerability does not apply.
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Determine installed Apache ActiveMQ versionCheck the ActiveMQ version by examining the lib directory for activemq-[version].jar, or run 'bin/activemq --version' if available, or check startup logs for the version number.Affected if You need the exact version number to compare against affected ranges.
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Compare version against affected rangesMatch your installed version against: < 5.19.2, >= 6.0.0 and <= 6.1.8, or exactly 6.2.0. Any match indicates the installation is within the affected version range.Affected if Your version falls into any of these ranges: < 5.19.2, 6.0.0 through 6.1.8, or exactly 6.2.0.
You are affected if your broker has an mqtt transportConnector enabled AND your ActiveMQ version is below 5.19.2, between 6.0.0-6.1.8, or exactly 6.2.0.
Generated from the published advisory. Verify against your own configuration.
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 · scoped5.19.2
Upgrade to Apache ActiveMQ version 5.19.2, 6.1.9, or 6.2.1 to obtain the fix. If immediate upgrade is not feasible, consider disabling mqtt transport connectors if not required.
5.19.2+ for 5.x line; 6.2.4+ for 6.x line
- 1. Identify the currently running Apache ActiveMQ version using bin/activemq --version or checking the version in the startup logs
- 2. For ActiveMQ 5.x users: If running version < 5.19.2, plan upgrade to 5.19.2 or later
- 3. For ActiveMQ 6.x users: If running version 6.0.0-6.1.8 or 6.2.0, plan upgrade to 6.2.4 or later (note: earlier 6.x fixes were missed per vendor advisory)
- 4. Before upgrading in production, test the new version in a staging environment
- 5. Backup existing ActiveMQ configuration files (conf/activemq.xml and any custom configuration)
- 6. Stop the ActiveMQ broker gracefully
- 7. Install the new version (5.19.2+ for 5.x line, or 6.2.4+ for 6.x line)
- 8. Restore or adapt configuration files to the new version
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Activemq
Scoped from the published advisory
- Consultation4.0 h
- Implementation8.0 h
- Testing8.0 h
- Review / QA4.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,656.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2025-66168 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2025-66168 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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