# CVE-2021-34566: WAGO I/O-Check Service prone to Memory Overflow

> Unauthenticated remote attackers can send crafted packets to crash the service and potentially execute code via memory overflow in WAGO I/O-Check Service.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/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:** 9 Nov 2022
- **Updated:** 1 May 2025
- **Also known as:** GHSA-xcqq-8632-69xx

## What is CVE-2021-34566?

CVE-2021-34566 is a critical memory corruption vulnerability in WAGO 750-81xx/xxx-xxxFW, published on 9 Nov 2022. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In WAGO I/O-Check Service in multiple products an unauthenticated remote attacker can send a specially crafted packet containing OS commands to crash the iocheck process and write memory resulting in loss of integrity and DoS.

Weakness: CWE-120 (Buffer Copy without Checking Size of Input)

## Which versions are affected by CVE-2021-34566?

It affects 49 products.


Products: Wago 750-8100 Firmware, Wago 750-8101\/025-000 Firmware, Wago 750-8101 Firmware, Wago 750-8102\/025-000 Firmware, Wago 750-8102 Firmware, Wago 750-8202\/000-011 Firmware, Wago 750-8202\/000-012 Firmware, Wago 750-8202\/000-022 Firmware, Wago 750-8202\/025-000 Firmware, Wago 750-8202\/025-001 Firmware, Wago 750-8202\/025-002 Firmware, Wago 750-8202\/040-000 Firmware, Wago 750-8202\/040-001 Firmware, Wago 750-8202 Firmware, Wago 752-8303\/8000-002 Firmware, Wago 762-4101 Firmware, Wago 762-4102 Firmware, Wago 762-4103 Firmware, Wago 762-4104 Firmware, Wago 762-4201\/8000-001 Firmware and 29 more.

## How do I fix CVE-2021-34566?

No fix has been published for CVE-2021-34566 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-34566 being exploited?

There is no known exploitation of CVE-2021-34566 in the wild and no public exploit code.

## Other vulnerabilities in WAGO 750-81xx/xxx-xxxFW

- [CVE-2021-34569](https://insights.sbomify.com/CVE-2021-34569/): WAGO I/O-Check Service prone to Out-of-bounds Write (critical 9.8)
- [CVE-2021-34567](https://insights.sbomify.com/CVE-2021-34567/): WAGO I/O-Check Service prone to Out-of-bounds Read (high 8.2)
- [CVE-2021-34568](https://insights.sbomify.com/CVE-2021-34568/): WAGO I/O-Check Service prone to Allocation of Resources Without Limits or Throttling (high 7.5)
- [CVE-2022-3281](https://insights.sbomify.com/CVE-2022-3281/): WAGO: multiple products - Loss of MAC-Address-Filtering after reboot (high 7.5)
- [CVE-2022-22511](https://insights.sbomify.com/CVE-2022-22511/): WAGO PLCs WBM vulnerable to reflected XSS (medium 5.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-34566 and fix it if it is affected.

What it is: CVE-2021-34566 is a critical memory corruption vulnerability in WAGO 750-81xx/xxx-xxxFW, published on 9 Nov 2022. 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-2021-34566 in the wild and no public exploit code.

Affected product: WAGO 750-81xx/xxx-xxxFW. 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-2021-34566/ (Markdown: https://insights.sbomify.com/CVE-2021-34566/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-34566
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-34566
- OSV: https://osv.dev/vulnerability/CVE-2021-34566

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-34566/
Summaries are generated and may contain mistakes; the official description above is the record.