# CVE-2025-40556: Denial of service in BACnet ATEC 550-440

> An attacker on the same BACnet network can cause a denial of service on Siemens ATEC devices by sending crafted MSTP messages, requiring a power cycle to recover.

- **Severity:** High 7.1 (`CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA: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:** 13 May 2025
- **Updated:** 13 May 2025
- **Also known as:** GHSA-c7rq-qv3j-63j3

## What is CVE-2025-40556?

CVE-2025-40556 is a high-severity denial of service vulnerability in Siemens BACnet ATEC 550-440, published on 13 May 2025. 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 BACnet ATEC 550-440 (All versions), BACnet ATEC 550-441 (All versions), BACnet ATEC 550-445 (All versions), BACnet ATEC 550-446 (All versions). Affected devices improperly handle specific incoming BACnet MSTP messages. This could allow an attacker residing in the same BACnet network to send a specially crafted MSTP message that results in a denial of service condition of the targeted device. A power cycle is required to restore the device's normal operation.

Weakness: CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2025-40556?


## How do I fix CVE-2025-40556?

No fix has been published for CVE-2025-40556 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-40556 being exploited?

There is no known exploitation of CVE-2025-40556 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40556 and fix it if it is affected.

What it is: CVE-2025-40556 is a high-severity denial of service vulnerability in Siemens BACnet ATEC 550-440, published on 13 May 2025. 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-2025-40556 in the wild and no public exploit code.

Affected product: Siemens BACnet ATEC 550-440. 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-2025-40556/ (Markdown: https://insights.sbomify.com/CVE-2025-40556/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40556
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40556
- OSV: https://osv.dev/vulnerability/CVE-2025-40556

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40556/
Summaries are generated and may contain mistakes; the official description above is the record.