HOMEVULNERABILITIESCVE-2020-27213
HIGH

CVE-2020-27213

CWE-330Published: October 10, 2023· Updated: Jun 17, 2026

7.5
CVSS v3.1

Official Description

An issue was discovered in Ethernut Nut/OS 5.1. The code that generates Initial Sequence Numbers (ISNs) for TCP connections derives the ISN from an insufficiently random source. As a result, an attacker may be able to determine the ISN of current and future TCP connections and either hijack existing ones or spoof future ones. While the ISN generator seems to adhere to RFC 793 (where a global 32-bit counter is incremented roughly every 4 microseconds), proper ISN generation should aim to follow at least the specifications outlined in RFC 6528.

NVD Source

Technical Analysis

CVE-2020-27213 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in full integrity compromise (data manipulation), with a CVSS base score of 7.5.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.None
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityNone
IntegrityHigh
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Affected Vendors & Products

ethernut1 product(s)
nut\/os
Source: NVD CPE · 1 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

ADVISORYhttps://www.cisa.gov/news-events/ics-advisories/icsa-21-042-01
ADVISORYhttps://www.forescout.com/resources/numberjack-weak-isn-generation-in-embedded-tcpip-stacks/
ADVISORYhttps://www.cisa.gov/news-events/ics-advisories/icsa-21-042-01
ADVISORYhttps://www.forescout.com/resources/numberjack-weak-isn-generation-in-embedded-tcpip-stacks/

All References (8)

→
http://lists.egnite.de/mailman/listinfo/en-nut-announceNot Applicable
→
http://www.ethernut.de/en/download/index.htmlRelease Notes
→
https://www.cisa.gov/news-events/ics-advisories/icsa-21-042-01Third Party Advisory · US Government Resource
→
https://www.forescout.com/resources/numberjack-weak-isn-generation-in-embedded-tcpip-stacks/Exploit · Third Party Advisory
→
http://lists.egnite.de/mailman/listinfo/en-nut-announceNot Applicable
→
http://www.ethernut.de/en/download/index.htmlRelease Notes
→
https://www.cisa.gov/news-events/ics-advisories/icsa-21-042-01Third Party Advisory · US Government Resource
→
https://www.forescout.com/resources/numberjack-weak-isn-generation-in-embedded-tcpip-stacks/Exploit · Third Party Advisory

Quick Facts

CVE IDCVE-2020-27213
CVSS Score7.5 / 10
SeverityHIGH
WeaknessCWE-330
CISA KEVNo
Affected1 vendor(s)
PublishedOct 10, 2023

Related CVEs (CWE-330)

CVE-2024-25943
9.8
CVE-2026-25072
9.8
CVE-2025-4607
9.8
CVE-2025-64097
9.8
CVE-2023-46740
9.8
CVE-2020-27630
9.8

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2020-27213 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWatch. CVE data is provided under the NVD usage policy.
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