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CVE-2021-21959

26
FAUCET Score

CVE-2021-21959 describes a critical misconfiguration in the MQTTS functionality of Sealevel Systems SeaConnect 370W v1.3.34, which significantly simplifies man-in-the-middle attacks. This vulnerability carries a high CVSS score of 8.1, indicating high impact on confidentiality, integrity, and availability, and can lead to full device control with high attack complexity but no user interaction required. While there is no known active exploitation or public exploit code (Metasploit, Nuclei, ExploitDB), the vulnerability has garnered some community discussion and media coverage, including an article from SecurityWeek highlighting its impact on ICS environments.

Impacted Technologies

VendorProductVersion(s)CPE
1.3.34CPE matchmatch criteria
cpe:2.3:o:sealevel:seaconnect_370w_firmware:1.3.34:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.0

7.7HIGH

CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:H

Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
LOW
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
2.2
Impact Score
5.5
CvssVersion
3.0

Exploit Intelligence

EPSS Score
0.84%
Probability of exploitation in next 30 days
EPSS Percentile
54.2%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0084 is in the 21st percentile among its peer group of 8,920 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.1 Bluesky, 0.1 Mastodon, and 0.2 GitHub mentions.

Media Mentions

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Remediation records are not available for this CVE.

References

talosintelligence.com / vulnerability_reports/TALOS-2021-1388
ExploitThird Party Advisory