CVE-2021-21959Network attack vector

Device control via disabled MQTTS certificate validation

Published Feb 4, 2022 · Updated Apr 15, 2025

Improper certificate validation in Sealevel SeaConnect 370W 1.3.34 allows man-in-the-middle attackers to control device functions over MQTTS. GetConnected calls NetworkConnectTLS without a certificate filename, causing the TLS socket to accept the supplied server certificate without validation. Interception of the device-to-SeaCloud connection is required and permits output changes, falsified input states, and malicious firmware delivery.

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

Improper certificate validation in Sealevel SeaConnect 370W 1.3.34 allows man-in-the-middle attackers to control device functions over MQTTS. GetConnected calls NetworkConnectTLS without a certificate filename, causing the TLS socket to accept the supplied server certificate without validation. Interception of the device-to-SeaCloud connection is required and permits output changes, falsified input states, and malicious firmware delivery.

The record

CVE
CVE-2021-21959
Published
Feb 4, 2022
Updated
Apr 15, 2025
Vendor
Sealevel Systems, Inc.
Product
SeaConnect 370W
Classifications
CWE-295, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 4, 2022CVE publishedPublication date reported by the CVE source.
  2. Apr 15, 2025Record 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=Sealevel Systems, Inc. SeaConnect 370W v1.3.34

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Sealevel Systems, Inc. · SeaConnect 370Wversion=Sealevel Systems, Inc. SeaConnect 370W v1.3.34

Published CVSS scores

7.7Cisco TalosCVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:H
8.1NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:P

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-295Improper Certificate Validation
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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