# CVE-2018-16561: Denial of service in SIMATIC S7-300 CPUs

> An attacker can cause a Denial-of-Service condition on SIMATIC S7-300 CPUs by sending specially crafted S7 communication packets, requiring a manual restart to recover.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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:** 17 Apr 2019
- **Updated:** 2 Jun 2026
- **Also known as:** GHSA-w9hm-m2x5-5x42

## What is CVE-2018-16561?

CVE-2018-16561 is a high-severity denial of service vulnerability in Siemens SIMATIC S7-300 CPUs, published on 17 Apr 2019. 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 S7-300 CPUs (All versions < V3.X.16). The affected CPUs improperly validate S7 communication packets which could cause a Denial-of-Service condition of the CPU. The CPU will remain in DEFECT mode until manual restart. Successful exploitation requires an attacker to be able to send a specially crafted S7 communication packet to a communication interface of the CPU. This includes Ethernet, PROFIBUS, and Multi Point Interfaces (MPI). No user interaction or privileges are required to exploit the security vulnerability. The vulnerability could allow causing a Denial-of-Service condition of the core functionality of the CPU, compromising the availability of the system. At the time of advisory publication no public exploitation of this security vulnerability was known. Siemens confirms the security vulnerability and provides mitigations to resolve the security issue.

Weakness: CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2018-16561?

It affects 4 products.


Products: Siemens Simatic S7-300 Firmware, Siemens Simatic S7-300f Firmware, Siemens Simatic S7-300fs Firmware, Siemens Simatic S7-300t Firmware.

## How do I fix CVE-2018-16561?

No fix has been published for CVE-2018-16561 yet. Limit exposure of the affected software until one is available.

## Is CVE-2018-16561 being exploited?

There is no known exploitation of CVE-2018-16561 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2018-16561 and fix it if it is affected.

What it is: CVE-2018-16561 is a high-severity denial of service vulnerability in Siemens SIMATIC S7-300 CPUs, published on 17 Apr 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-2018-16561 in the wild and no public exploit code.

Affected product: Siemens SIMATIC S7-300 CPUs. 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-2018-16561/ (Markdown: https://insights.sbomify.com/CVE-2018-16561/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2018-16561
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2018-16561
- OSV: https://osv.dev/vulnerability/CVE-2018-16561

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From sbomify Insights: https://insights.sbomify.com/CVE-2018-16561/
Summaries are generated and may contain mistakes; the official description above is the record.