CVE-2026-120596
Received Received - Intake

Denial-of-Service in Nut/OS TCP/IP Stack

Publication date: 2026-11-02

Last updated on: 2026-11-02

Assigner: CERT/CC

Description
A remotely exploitable denial-of-service vulnerability exists in the TCP options parser of the Nut/Net TCP/IP stack included in Nut/OS, developed by Ethernut/Egnite. Nut/OS releases up to version 5.1 are affected. An unauthenticated attacker can send a single TCP segment containing an unknown TCP option with a length byte of zero to any open TCP port on a vulnerable device. When processed, this malformed option triggers an infinite loop in the function NutTcpInputOptions, permanently blocking the TCP processing thread and rendering all TCP-based services unresponsive until the device is rebooted.

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Meta Information

Published
2026-11-02
Last Modified
2026-11-02
Generated
2026-11-02
AI Q&A
2026-11-02
EPSS Evaluated
N/A
NVD
CVE-2026-120596

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
Ethernut / egnite GmbH Nut/Net TCP/IP Stack Nut/OS 5.1

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Exploitability

CWE
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KEV
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CWE ID Description
CWE-835 The product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop.

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Executive Summary

This is a remotely exploitable denial-of-service vulnerability in the TCP options parser of the Nut/Net TCP/IP stack used in Nut/OS. It affects versions up to 5.1. An attacker can send a single TCP segment with an unknown option and a zero-length byte to any open TCP port. This causes an infinite loop in the NutTcpInputOptions function, freezing the TCP processing thread and making all TCP services unresponsive until the device is rebooted.

Detection Guidance

Detecting this vulnerability requires monitoring for malformed TCP segments with unknown options and zero-length bytes. Use network tools like tcpdump or Wireshark to capture and analyze TCP traffic for suspicious packets. Check for devices running Nut/OS versions up to 5.1 by inspecting system logs or firmware versions.

Impact Analysis

If you use a vulnerable Nut/OS device with TCP/IP services exposed to a network, an attacker could exploit this flaw to crash the device. This would disrupt all network-dependent functions, such as remote management, data transfers, or internet connectivity, until the device is manually rebooted. It does not require authentication or multiple requests, making it easy to trigger.

Compliance Impact

This vulnerability could lead to service disruptions, data unavailability, or prolonged downtime, which may violate compliance requirements for availability in standards like GDPR or HIPAA. If the affected device handles sensitive data, prolonged downtime could result in data processing interruptions, potentially breaching regulatory obligations for timely access or processing.

Mitigation Strategies

Immediately update Nut/OS to a version beyond 5.1 if available. Block or filter TCP segments with unknown options at the network perimeter using firewalls or intrusion prevention systems. Disable unnecessary TCP ports on vulnerable devices to reduce attack surface.

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