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CVE-2020-27213

22
FAUCET Score

CVE-2020-27213 describes a vulnerability in Ethernut Nut/OS 5.1 where the TCP Initial Sequence Number (ISN) generation uses an insufficiently random source, making ISNs predictable. This flaw allows attackers to determine current and future ISNs, potentially leading to TCP connection hijacking or spoofing. With a CVSS score of 7.5 (High), the vulnerability is network-exploitable with low attack complexity, impacting integrity by allowing unauthorized modification of data. There is no evidence of active exploitation, nor are there publicly available exploit modules in Metasploit or Nuclei, despite some community discussion and media coverage.

Impacted Technologies

VendorProductVersion(s)CPE
5.1CPE matchmatch criteria
cpe:2.3:o:ethernut:nut\/os:5.1:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

7.5HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
HIGH
Availability Impact
NONE
Exploitability Score
3.9
Impact Score
3.6
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.97%
Probability of exploitation in next 30 days
EPSS Percentile
58.3%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0097 is in the 33rd percentile among its peer group of 51,506 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.1 Mastodon, and 0.4 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

lists.egnite.de / mailman/listinfo/en-nut-announce
Not Applicable
cisa.gov / news-events/ics-advisories/icsa-21-042-01
Third Party AdvisoryUS Government Resource
forescout.com / resources/numberjack-weak-isn-generation-in-embedded-tcpip-stacks
ExploitThird Party Advisory
ethernut.de / en/download/index.html
Release Notes