CVE-2020-27213

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.

• CWE-330

• 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

Published

Oct 10, 2023

Last Modified

Jun 17, 2026

Status

Modified

• How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
• Autonomous PentestingAI agents that find and validate exploitable vulnerabilities like this one across your applications.
• PR ReviewsPentest every pull request so vulnerable code is caught before it ships to production.
• AI Penetration TestingHow AI-driven penetration testing continuously covers your attack surface.

• CVE-2020-27207Zetetic SQLCipher 4.x before 4.4.1 has a use-after-free, rel…7.5
• CVE-2020-27208The flash read-out protection (RDP) level is not enforced du…6.8
• CVE-2020-27209The ECDSA operation of the micro-ecc library 1.0 is vulnerab…7.5
• CVE-2020-2721Vulnerability in the Oracle FLEXCUBE Investor Servicing prod…6.5
• CVE-2020-27211Nordic Semiconductor nRF52840 devices through 2020-10-19 hav…5.7
• CVE-2020-27212STMicroelectronics STM32L4 devices through 2020-10-19 have i…7
• CVE-2020-27216In Eclipse Jetty versions 1.0 thru 9.4.32.v20200930, 10.0.0.…7
• CVE-2020-27217In Eclipse Hono version 1.3.0 and 1.4.0 the AMQP protocol ad…7.5
• CVE-2020-27218In Eclipse Jetty version 9.4.0.RC0 to 9.4.34.v20201102, 10.0…4.8
• CVE-2020-27219In all version of Eclipse Hawkbit prior to 0.3.0M7, the HTTP…6.1
• CVE-2020-2722Vulnerability in the Oracle FLEXCUBE Investor Servicing prod…5.4
• CVE-2020-27220The Eclipse Hono AMQP and MQTT protocol adapters do not chec…8.8