# CVE-2021-33737: Denial of service in SIMATIC CP 343-1 (incl. SIPLUS variants)

> A remote attacker can cause a denial of service on Siemens SIMATIC communication processors by sending a specially crafted packet to port 102/tcp.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:P/RL:U/RC:C`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 14 Sep 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-w34c-jjqq-3824

## What is CVE-2021-33737?

CVE-2021-33737 is a high-severity denial of service vulnerability in Siemens SIMATIC CP 343-1 (incl. SIPLUS variants), published on 14 Sep 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A vulnerability has been identified in SIMATIC CP 343-1 (incl. SIPLUS variants) (All versions), SIMATIC CP 343-1 Advanced (incl. SIPLUS variants) (All versions), SIMATIC CP 343-1 ERPC (All versions), SIMATIC CP 343-1 Lean (incl. SIPLUS variants) (All versions), SIMATIC CP 443-1 (All versions < V3.3), SIMATIC CP 443-1 (All versions < V3.3), SIMATIC CP 443-1 Advanced (All versions < V3.3), SIPLUS NET CP 443-1 (All versions < V3.3), SIPLUS NET CP 443-1 Advanced (All versions < V3.3). Sending a specially crafted packet to port 102/tcp of an affected device could cause a denial of service condition. A restart is needed to restore normal operations.

Weakness: CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer)

## Which versions are affected by CVE-2021-33737?

It affects 6 products.


Products: Siemens Simatic Cp 343-1 Advanced Firmware, Siemens Simatic Cp 343-1 Erpc Firmware, Siemens Simatic Cp 343-1 Firmware, Siemens Simatic Cp 343-1 Lean Firmware, Siemens Simatic Cp 443-1 Advanced Firmware, Siemens Simatic Cp 443-1 Firmware.

## How do I fix CVE-2021-33737?

No fix has been published for CVE-2021-33737 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-33737 being exploited?

There is no known exploitation of CVE-2021-33737 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-33737 and fix it if it is affected.

What it is: CVE-2021-33737 is a high-severity denial of service vulnerability in Siemens SIMATIC CP 343-1 (incl. SIPLUS variants), published on 14 Sep 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-2021-33737 in the wild and no public exploit code.

Affected product: Siemens SIMATIC CP 343-1 (incl. SIPLUS variants). 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-2021-33737/ (Markdown: https://insights.sbomify.com/CVE-2021-33737/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-33737
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-33737
- OSV: https://osv.dev/vulnerability/CVE-2021-33737

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From sbomify Insights: https://insights.sbomify.com/CVE-2021-33737/
Summaries are generated and may contain mistakes; the official description above is the record.