CVE-2020-27213

What it is

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.

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of data tampering.

Exploit odds

1.0% chance of exploitation in the next 30 days (EPSS).

Fix

No patch or advisory is linked yet. Look at mitigations or restrict exposure.

Timeline

1. 2023-10-10 17:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 03:08 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 1.0% in the next 30 days (EPSS).
• Severity: 7.5 HIGH (CVSS).
• Fix: none linked yet, which raises it.

Details

Published

2023-10-10 17:15 UTC

Last modified

2026-06-17 03:08 UTC

Exploit probability

1.0% · EPSS, next 30 days

Weakness

CWE-330

Record status

Modified

Affected

• Ethernut nut\/os 5.1

Attack profile CVSS 3.1 · 7.5

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

High

Availability

None

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2020-27213.md and follow it. Check whether this project is affected by CVE-2020-27213. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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