CVE-2021-21968Public exploitNetwork attack vector

Arbitrary file overwrite via unvalidated OTA destination

Published Feb 4, 2022 · Updated Apr 15, 2025

Arbitrary file overwrite in Sealevel Systems SeaConnect 370W 1.3.34 allows man-in-the-middle attackers to replace device files via MQTT. The OTA update task passes the unvalidated MQTT dest value to sl_extlib_FlcOpenFile, then writes FTP(S)-retrieved content before size and CRC checks. Exploitation requires interception of the device's MQTTS command channel; overwriting /usr/settings.bin with the documented payload sets a known HTTP password and enables arbitrary HTTP requests.

CVSS severity8.1
High
EPSS probability0.95%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Arbitrary file overwrite in Sealevel Systems SeaConnect 370W 1.3.34 allows man-in-the-middle attackers to replace device files via MQTT. The OTA update task passes the unvalidated MQTT dest value to sl_extlib_FlcOpenFile, then writes FTP(S)-retrieved content before size and CRC checks. Exploitation requires interception of the device's MQTTS command channel; overwriting /usr/settings.bin with the documented payload sets a known HTTP password and enables arbitrary HTTP requests.

The record

CVE
CVE-2021-21968
Published
Feb 4, 2022
Updated
Apr 15, 2025
Vendor
Sealevel Systems, Inc.
Product
SeaConnect 370W
Classifications
CWE-20, T1565.002
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

8.1Cisco TalosCVSS:3.0/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
8.3NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/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.

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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 exploitPublished

Weakness, pattern, technique

CWE-20Improper Input Validation
T1565.002Transmitted Data Manipulation

Public exploit references

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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