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.
References (4)
Core 4
Core References
Not Applicable
http://lists.egnite.de/mailman/listinfo/en-nut-announce
Release Notes
http://www.ethernut.de/en/download/index.html
Third Party Advisory, US Government Resource
https://www.cisa.gov/news-events/ics-advisories/icsa-21-042-01
Exploit, Third Party Advisory
https://www.forescout.com/resources/numberjack-weak-isn-generation-in-embedded-tcpip-stacks/
Scores
CVSS v3
7.5
EPSS
0.0097
EPSS Percentile
57.2%
Attack Vector
NETWORK
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
CISA SSVC
Vulnrichment
Exploitation
none
Automatable
yes
Technical Impact
partial
Details
CWE
CWE-330
Status
published
Products (1)
ethernut/nut\/os
5.1
Published
Oct 10, 2023
Tracked Since
Feb 18, 2026