---
title: "CVE-2026-120596: Ethernut Nut/OS - Denial of Service"
description: "Ethernut Nut/OS <= 5.1 contains a denial-of-service caused by a malformed TCP option with zero length in NutTcpInputOptions, letting unauthenticated remote attackers block TCP services, exploit requires sending crafted TCP segment."
url: https://panop.io/threat-heartbeat/CVE-2026-120596/
---

# CVE-2026-120596 Ethernut Nut/OS - Denial of Service

Ethernut Nut/OS <= 5.1 contains a denial-of-service caused by a malformed TCP option with zero length in NutTcpInputOptions, letting unauthenticated remote attackers block TCP services, exploit requires sending crafted TCP segment.

CVSS base score 7.5 /10

High

CISA KEV

Not listed

Public exploit

None known

Authentication

Not required

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-120596)

## Details

Type

Denial of Service

Impact

Denial Of Service

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Published

2 November 2026

Updated

3 November 2026

Weakness

[CWE-835](https://cwe.mitre.org/data/definitions/835.html)

## Vendor fix

Update to the latest version beyond 5.1.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-120596](https://nvd.nist.gov/vuln/detail/CVE-2026-120596)
- [https://www.ethernut.de/en/download/index.html](https://www.ethernut.de/en/download/index.html)

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## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

Panop answers these inside your environment, for this CVE and every other finding.

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