# CVE-2019-6821: Weak cryptography in Modicon Controllers, Modicon M580 firmware versions prior to V2.30, and all firmware versions of Modicon M340, Modicon Premium, Modicon Quantum

> Insufficiently random values in Modicon PLC firmware allow attackers to hijack TCP connections via Ethernet communication.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/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:** 22 May 2019
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-pr9h-xjrf-gjcr

## What is CVE-2019-6821?

CVE-2019-6821 is a medium-severity vulnerability in Modicon Controllers, Modicon M580 firmware versions prior to V2.30, and all firmware versions of Modicon M340, Modicon Premium, Modicon Quantum, published on 22 May 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

CWE-330: Use of Insufficiently Random Values vulnerability, which could cause the hijacking of the TCP connection when using Ethernet communication in Modicon M580 firmware versions prior to V2.30, and all firmware versions of Modicon M340, Modicon Premium, Modicon Quantum.

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

## Which versions are affected by CVE-2019-6821?

It affects 4 products.


Products: Schneider-Electric Modicon M340 Firmware, Schneider-Electric Modicon M580 Firmware, Schneider-Electric Modicon Premium Firmware, Schneider-Electric Modicon Quantum Firmware.

## How do I fix CVE-2019-6821?

No fix has been published for CVE-2019-6821 yet. Limit exposure of the affected software until one is available.

## Is CVE-2019-6821 being exploited?

There is no known exploitation of CVE-2019-6821 in the wild and no public exploit code.

## Other vulnerabilities in Modicon Controllers, Modicon M580 firmware versions prior to V2.30, and all firmware versions of Modicon M340, Modicon Premium, Modicon Quantum

- [CVE-2018-7842](https://insights.sbomify.com/CVE-2018-7842/): Auth bypass in Modicon M580 Modicon M340 Modicon Quantum Modicon Premium (critical 9.8)
- [CVE-2018-7846](https://insights.sbomify.com/CVE-2018-7846/): Auth bypass in Modicon M580 Modicon M340 Modicon Quantum Modicon Premium (critical 9.8)
- [CVE-2018-7847](https://insights.sbomify.com/CVE-2018-7847/): Missing authorization in Modicon M580 Modicon M340 Modicon Quantum Modicon Premium (critical 9.8)
- [CVE-2019-6808](https://insights.sbomify.com/CVE-2019-6808/): Missing authorization in Modicon M580 Modicon M340 Modicon Quantum Modicon Premium (critical 9.8)
- [CVE-2019-6845](https://insights.sbomify.com/CVE-2019-6845/): Information disclosure in Modicon M580, Modicon M340, Modicon Premium , Modicon Quantum (all firmware versions) (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2019-6821 and fix it if it is affected.

What it is: CVE-2019-6821 is a medium-severity vulnerability in Modicon Controllers, Modicon M580 firmware versions prior to V2.30, and all firmware versions of Modicon M340, Modicon Premium, Modicon Quantum, published on 22 May 2019. 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-2019-6821 in the wild and no public exploit code.

Affected product: Modicon Controllers, Modicon M580 firmware versions prior to V2.30, and all firmware versions of Modicon M340, Modicon Premium, Modicon Quantum. 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-2019-6821/ (Markdown: https://insights.sbomify.com/CVE-2019-6821/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2019-6821
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2019-6821
- OSV: https://osv.dev/vulnerability/CVE-2019-6821

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From sbomify Insights: https://insights.sbomify.com/CVE-2019-6821/
Summaries are generated and may contain mistakes; the official description above is the record.