# CVE-2021-37186: Weak cryptography in LOGO! CMR2020

> Weak random number generation in TCP/IP stack allows adjacent attackers to spoof connections and access sensitive information on Siemens industrial devices.

- **Severity:** Medium 5.4 (`CVSS:3.1/AV:A/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:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 14 Sep 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-5g5j-x767-23r3

## What is CVE-2021-37186?

CVE-2021-37186 is a medium-severity vulnerability in Siemens LOGO! CMR2020, published on 14 Sep 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A vulnerability has been identified in LOGO! CMR2020 (All versions < V2.2), LOGO! CMR2040 (All versions < V2.2), SIMATIC RTU3010C (All versions < V4.0.9), SIMATIC RTU3030C (All versions < V4.0.9), SIMATIC RTU3031C (All versions < V4.0.9), SIMATIC RTU3041C (All versions < V4.0.9). The underlying TCP/IP stack does not properly calculate the random numbers used as ISN (Initial Sequence Numbers). An adjacent attacker with network access to the LAN interface could interfere with traffic, spoof the connection and gain access to sensitive information.

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

## Which versions are affected by CVE-2021-37186?

It affects 6 products.


Products: Siemens Logo\! Cmr2020 Firmware, Siemens Logo\! Cmr2040 Firmware, Siemens Simatic Rtu3010c Firmware, Siemens Simatic Rtu3030c Firmware, Siemens Simatic Rtu3031c Firmware, Siemens Simatic Rtu3041c Firmware.

## How do I fix CVE-2021-37186?

No fix has been published for CVE-2021-37186 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-37186 being exploited?

There is no known exploitation of CVE-2021-37186 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-37186 and fix it if it is affected.

What it is: CVE-2021-37186 is a medium-severity vulnerability in Siemens LOGO! CMR2020, published on 14 Sep 2021. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-37186 in the wild and no public exploit code.

Affected product: Siemens LOGO! CMR2020. 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-2021-37186/ (Markdown: https://insights.sbomify.com/CVE-2021-37186/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-37186
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-37186
- OSV: https://osv.dev/vulnerability/CVE-2021-37186

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-37186/
Summaries are generated and may contain mistakes; the official description above is the record.