# CVE-2017-6026: Weak cryptography in Schneider Electric Modicon PLCs

> Insufficiently random session numbers in Schneider Electric Modicon PLCs allow attackers to compromise active user sessions.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/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:** 30 Jun 2017
- **Updated:** 5 Aug 2024
- **Also known as:** GHSA-c4x2-m5w5-m3rx

## What is CVE-2017-6026?

CVE-2017-6026 is a critical vulnerability in Schneider Electric Modicon PLCs, published on 30 Jun 2017. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A Use of Insufficiently Random Values issue was discovered in Schneider Electric Modicon PLCs Modicon M241, firmware versions prior to Version 4.0.5.11, and Modicon M251, firmware versions prior to Version 4.0.5.11. The session numbers generated by the web application are lacking randomization and are shared between several users. This may allow a current session to be compromised.

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

## Which versions are affected by CVE-2017-6026?

It affects 2 products.


Products: Schneider-Electric Modicon M241 Firmware, Schneider-Electric Modicon M251 Firmware.

## How do I fix CVE-2017-6026?

No fix has been published for CVE-2017-6026 yet. Limit exposure of the affected software until one is available.

## Is CVE-2017-6026 being exploited?

There is no known exploitation of CVE-2017-6026 in the wild and no public exploit code.

Public exploit code:

- Schneider Electric PLC - Session Calculation Authentication Bypass (exploitdb)

## Other vulnerabilities in Schneider Electric Modicon PLCs

- [CVE-2017-6028](https://insights.sbomify.com/CVE-2017-6028/): Hardcoded credentials in Schneider Electric Modicon PLCs (critical 9.8)
- [CVE-2021-22699](https://insights.sbomify.com/CVE-2021-22699/): Denial of service in Modicon M241/M251 logic controllers firmware prior to V5.1.9.1 (high 7.5)
- [CVE-2025-13901](https://insights.sbomify.com/CVE-2025-13901/): Denial of service in Modicon M241/M251 (medium 6.9)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2017-6026 and fix it if it is affected.

What it is: CVE-2017-6026 is a critical vulnerability in Schneider Electric Modicon PLCs, published on 30 Jun 2017. 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-2017-6026 in the wild and no public exploit code.

Affected product: Schneider Electric Modicon PLCs. 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-2017-6026/ (Markdown: https://insights.sbomify.com/CVE-2017-6026/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2017-6026
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2017-6026
- OSV: https://osv.dev/vulnerability/CVE-2017-6026

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From sbomify Insights: https://insights.sbomify.com/CVE-2017-6026/
Summaries are generated and may contain mistakes; the official description above is the record.