CVE-2026-8686
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 · uneditedMissing bounds validation in the MQTT v5.0 property parser in coreMQTT before 5.0.1 allows an MQTT broker to cause a denial of service by sending a crafted packet. To remediate this issue, users should upgrade to v5.0.1.
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 confidenceMissing bounds validation in the MQTT v5.0 property parser in coreMQTT allows a malicious broker to send crafted packets with malformed properties that trigger an out-of-bounds read/write, causing denial of service.
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= 5.0.0CVSS 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
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/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 checksWork through these to decide whether this CVE applies to you.
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Identify coreMQTT library presenceSearch for coreMQTT library files in your project dependencies, typically found in package managers (e.g., npm, pip, conan) or as a submodule in FreeRTOS projectsAffected if coreMQTT library is present in the project
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Determine installed coreMQTT versionRun the package manager command to inspect the installed version, such as 'npm list coremqtt', 'pip show coremqtt', or check the version.h/CHANGELOG file within the library directoryAffected if The version reported is exactly 5.0.0
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Verify MQTT v5.0 protocol usageInspect your MQTT client initialization code for the protocol version setting - look for parameters like mqtt5, protocolVersion: 5, or MQTT_VERSION_5 in the client configurationAffected if MQTT v5.0 protocol is explicitly enabled in the client configuration
You are affected only if your project uses coreMQTT version 5.0.0 AND has MQTT v5.0 protocol enabled, as the vulnerability exists in the v5.0 property parser specifically.
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 · scopedUpgrade coreMQTT to version 5.0.1 or later which adds proper bounds validation to the property parser.
coreMQTT v5.0.1
- Update coreMQTT library to version 5.0.1
- Verify the update was successful by checking the library version
- Rebuild and redeploy any applications using this library
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation4.0 h
- Testing5.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,568.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-8686 — 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-2026-8686 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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- 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
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