# CVE-2025-40820: Denial of service in SIDOOR ATD430W

> Unauthenticated remote attackers can cause denial of service in Siemens industrial devices by exploiting weak TCP sequence number validation.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/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:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 9 Dec 2025
- **Updated:** 9 Dec 2025
- **Also known as:** GHSA-84r6-pwmm-h2fw

## What is CVE-2025-40820?

CVE-2025-40820 is a high-severity denial of service vulnerability in Siemens SIDOOR ATD430W, published on 9 Dec 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Affected products do not properly enforce TCP sequence number validation in specific scenarios but accept values within a broad range. This could allow an unauthenticated remote attacker e.g. to interfere with connection setup, potentially leading to a denial of service. The attack succeeds only if an attacker can inject IP packets with spoofed addresses at precisely timed moments, and it affects only TCP-based services.

Weakness: CWE-940 (Improper Verification of Source of a Communication Channel)

## Which versions are affected by CVE-2025-40820?


## How do I fix CVE-2025-40820?

No fix has been published for CVE-2025-40820 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-40820 being exploited?

There is no known exploitation of CVE-2025-40820 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40820 and fix it if it is affected.

What it is: CVE-2025-40820 is a high-severity denial of service vulnerability in Siemens SIDOOR ATD430W, published on 9 Dec 2025. 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-2025-40820 in the wild and no public exploit code.

Affected product: Siemens SIDOOR ATD430W. 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-2025-40820/ (Markdown: https://insights.sbomify.com/CVE-2025-40820/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40820
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40820
- OSV: https://osv.dev/vulnerability/CVE-2025-40820

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40820/
Summaries are generated and may contain mistakes; the official description above is the record.