# CVE-2020-27213: Weak cryptography in n/a

> Insufficiently random TCP Initial Sequence Numbers in Ethernut Nut/OS allow attackers to hijack existing connections or spoof future ones.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 10 Oct 2023
- **Updated:** 19 Sep 2024
- **Also known as:** GHSA-5wm2-v84q-jw9v

## What is CVE-2020-27213?

CVE-2020-27213 is a high-severity vulnerability in n/a, published on 10 Oct 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-330 (Use of Insufficiently Random Values)

## Which versions are affected by CVE-2020-27213?

It affects 1 product.


Products: Ethernut Nut\/Os.

## How do I fix CVE-2020-27213?

No fix has been published for CVE-2020-27213 yet. Limit exposure of the affected software until one is available.

## Is CVE-2020-27213 being exploited?

There is no known exploitation of CVE-2020-27213 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2020-25107](https://insights.sbomify.com/CVE-2020-25107/): Memory corruption in n/a (critical 9.8)
- [CVE-2020-25108](https://insights.sbomify.com/CVE-2020-25108/): Memory corruption in n/a (critical 9.8)
- [CVE-2020-25109](https://insights.sbomify.com/CVE-2020-25109/): Denial of service in n/a (critical 9.8)
- [CVE-2020-25110](https://insights.sbomify.com/CVE-2020-25110/): Memory corruption in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-27213 and fix it if it is affected.

What it is: CVE-2020-27213 is a high-severity vulnerability in n/a, published on 10 Oct 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2020-27213 in the wild and no public exploit code.

Affected product: n/a. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2020-27213/ (Markdown: https://insights.sbomify.com/CVE-2020-27213/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-27213
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-27213
- OSV: https://osv.dev/vulnerability/CVE-2020-27213

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-27213/
Summaries are generated and may contain mistakes; the official description above is the record.