CVE-2021-27662Network attack vector

Unauthenticated command replay via captured TCP packets

Published Sep 15, 2021 · Updated Sep 17, 2024

Authentication bypass in Johnson Controls Kantech KT-1 3.01 and earlier allows remote attackers to replay controller commands. The controller accepts a previously captured TCP command message as authentic instead of rejecting reused traffic. Network access sufficient to capture traffic is required, and the vendor does not specify which door-control commands can be replayed.

CVSS severity8.1
High
EPSS probability0.84%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in Johnson Controls Kantech KT-1 3.01 and earlier allows remote attackers to replay controller commands. The controller accepts a previously captured TCP command message as authentic instead of rejecting reused traffic. Network access sufficient to capture traffic is required, and the vendor does not specify which door-control commands can be replayed.

The record

CVE
CVE-2021-27662
Published
Sep 15, 2021
Updated
Sep 17, 2024
Vendor
Johnson Controls
Product
Kantech KT-1
Classifications
CWE-294, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 15, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 17, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=all versions up to and including 3.01 <=3.01

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Johnson Controls · Kantech KT-1version=all versions up to and including 3.01 <=3.01

Published CVSS scores

8.6Johnson ControlsCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L
6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:P
8.1NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-294Authentication Bypass by Capture-replay
T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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