CVE-2021-27662
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 · uneditedThe KT-1 door controller is susceptible to replay or man-in-the-middle attacks where an attacker can record and replay TCP packets. This issue affects Johnson Controls KT-1 all versions up to and including 3.01
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 · moderate confidenceThe Johnson Controls KT-1 door controller lacks replay protection or cryptographic authentication for TCP communications, allowing an attacker to capture and replay valid packets to gain unauthorized physical access.
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<= 3.01CVSS 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
- High
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:H/PR:N/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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Confirm device modelIdentify whether the target system is a Johnson Controls Kantech KT-1 Door Controller through network scanning, device inventory, or management consoleAffected if Device is a KT-1 Door Controller
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Check firmware versionAccess the controller's web interface, serial console, or management software to retrieve the installed firmware versionAffected if Firmware version is 3.01 or lower
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Verify TCP communication is enabledExamine the controller's network settings or configuration to determine if TCP-based communication for door access operations is activeAffected if TCP communications are enabled and exposed on the network
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Inspect replay protection configurationReview the controller's security or communication settings to check whether time-based nonces, sequence numbers, or cryptographic authentication are implemented for TCP sessionsAffected if No replay protection or cryptographic authentication is configured for TCP traffic
The environment is affected if the device is a KT-1 controller running firmware 3.01 or lower with TCP communications enabled and no replay protection or cryptographic authentication in place.
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.
From vendor dataImplement cryptographic session validation (e.g., time-based nonces, sequence numbers, or TLS) to prevent replay; coordinate with Johnson Controls for firmware updates; network-segment the door controller to limit exposure.
- Consultation8.0 h
- Implementation12.0 h
- Testing8.0 h
- Review / QA6.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-27662 — 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-2021-27662 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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