TI-2020-16541 Aliases CVE-2020-27213 GHSA-5wm2-v84q-jw9v

An issue was discovered in Ethernut Nut/OS 5.1.

MEDIUM 41CWE-330Published 2023-10-10 · Updated 2024-09-19

Key facts

Attack vector: Network
Privileges required: None
User interaction: None
Attack complexity: Low
Impact type: —
Confidentiality · integrity · availability: None · High · None
Fix status: No fix listed

Attack profile from CVSS 3.1 · NVD. Fix status from CNA.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV

EPSS 0.00973 62nd percentileScored 2026-11-07

Public exploit Yes 1 exploit referenceTagged by NVD

Fix No fix listed No fixed version in the sources yet

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: None
Automatable: Yes
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
—	—	all versions	—	No fix listed	CNA

— Vendor— Affected all versions Fixed in — No fix listed CNA

CPE configurations NVD · 1

CPE	Versions	Role	Vendor
cpe:2.3:o:ethernut:nut\/os:5.1:::::::*	5.1	Vulnerable	Ethernut

cpe:2.3:o:ethernut:nut\/os:5.1:*:*:*:*:*:*:* Versions 5.1 Vulnerable ·Ethernut

Remediation

No fixed version listed by the sources yet.

Timeline

2026-10-02 Threatist record created from CVE-2020-27213
2026-10-03 Alias added: GHSA-5wm2-v84q-jw9v

References

Exploit 1

https://www.forescout.com/resources/numberjack-weak-isn-generation-in-embedded-tcpip-stacks/

Advisory 1

https://www.cisa.gov/news-events/ics-advisories/icsa-21-042-01

Other 2

TI-2020-15358 An issue was discovered in the DNS implementation in Ethernut in Nut/OS 5.1. CVSS 3.1CRITICAL 9.8
TI-2020-15357 An issue was discovered in the DNS implementation in Ethernut in Nut/OS 5.1. CVSS 3.1CRITICAL 9.8
TI-2020-15356 An issue was discovered in the DNS implementation in Ethernut in Nut/OS 5.1. CVSS 3.1CRITICAL 9.8
TI-2020-15355 An issue was discovered in the DNS implementation in Ethernut in Nut/OS 5.1. CVSS 3.1CRITICAL 9.8

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences