# CVE-2021-31337: Missing authorization in SINAMICS Medium Voltage Products

> Remote attackers can access SIMATIC HMI devices without authentication if the Telnet service is enabled, requiring configuration changes to mitigate.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 28 Jun 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-hwxw-fmr7-f2c3

## What is CVE-2021-31337?

CVE-2021-31337 is a critical missing authorization vulnerability in SINAMICS Medium Voltage Products, published on 28 Jun 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

The Telnet service of the SIMATIC HMI Comfort Panels system component in affected products does not require authentication, which may allow a remote attacker to gain access to the device if the service is enabled. Telnet is disabled by default on the SINAMICS Medium Voltage Products (SINAMICS SL150: All versions, SINAMICS SM150: All versions, SINAMICS SM150i: All versions).

Weakness: CWE-306 (Missing Authentication for Critical Functionality)

## Which versions are affected by CVE-2021-31337?

It affects 3 products.


Products: Siemens Sinamics Sl150 Firmware, Siemens Sinamics Sm150 Firmware, Siemens Sinamics Sm150i Firmware.

## How do I fix CVE-2021-31337?

No fix has been published for CVE-2021-31337 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-31337 being exploited?

There is no known exploitation of CVE-2021-31337 in the wild and no public exploit code.

## Other vulnerabilities in SINAMICS Medium Voltage Products

- [CVE-2021-27388](https://insights.sbomify.com/CVE-2021-27388/): Missing authorization in SINAMICS Medium Voltage Products, Remote Access (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-31337 and fix it if it is affected.

What it is: CVE-2021-31337 is a critical missing authorization vulnerability in SINAMICS Medium Voltage Products, published on 28 Jun 2021. 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-2021-31337 in the wild and no public exploit code.

Affected product: SINAMICS Medium Voltage Products. 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-2021-31337/ (Markdown: https://insights.sbomify.com/CVE-2021-31337/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-31337
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-31337
- OSV: https://osv.dev/vulnerability/CVE-2021-31337

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-31337/
Summaries are generated and may contain mistakes; the official description above is the record.