# CVE-2021-34586: CODESYS V2 web server: crafted requests could trigger a null pointer dereference (DoS)

> Crafted requests to the CODESYS V2 web server can trigger a null pointer dereference, causing a denial-of-service condition.

- **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:** 26 Oct 2021
- **Updated:** 17 Sep 2024
- **Also known as:** GHSA-hmwx-8xfx-mg6m

## What is CVE-2021-34586?

CVE-2021-34586 is a high-severity vulnerability in CODESYS V2, published on 26 Oct 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the CODESYS V2 web server prior to V1.1.9.22 crafted web server requests may cause a Null pointer dereference in the CODESYS web server and may result in a denial-of-service condition.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2021-34586?

It affects 28 products.


Products: Codesys Codesys, Wago 750-8202 Firmware, Wago 750-8203 Firmware, Wago 750-8204 Firmware, Wago 750-8206 Firmware, Wago 750-8207 Firmware, Wago 750-8208 Firmware, Wago 750-8210 Firmware, Wago 750-8211 Firmware, Wago 750-8212 Firmware, Wago 750-8213 Firmware, Wago 750-8214 Firmware, Wago 750-8216 Firmware, Wago 750-8217 Firmware, Wago 750-823 Firmware, Wago 750-829 Firmware, Wago 750-831 Firmware, Wago 750-832 Firmware, Wago 750-852 Firmware, Wago 750-862 Firmware and 8 more.

## How do I fix CVE-2021-34586?

No fix has been published for CVE-2021-34586 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-34586 being exploited?

There is no known exploitation of CVE-2021-34586 in the wild and no public exploit code.

## Other vulnerabilities in CODESYS V2

- [CVE-2019-16265](https://insights.sbomify.com/CVE-2019-16265/): Memory corruption in n/a (critical 9.8)
- [CVE-2021-34584](https://insights.sbomify.com/CVE-2021-34584/): CODESYS V2 web server: crafted requests could trigger a buffer over-read (DoS) (critical 9.1)
- [CVE-2021-21869](https://insights.sbomify.com/CVE-2021-21869/): Deserialization in CODESYS (high 8.8)
- [CVE-2021-21867](https://insights.sbomify.com/CVE-2021-21867/): Deserialization in CODESYS (high 8.8)
- [CVE-2021-21868](https://insights.sbomify.com/CVE-2021-21868/): Deserialization in CODESYS (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-34586 and fix it if it is affected.

What it is: CVE-2021-34586 is a high-severity vulnerability in CODESYS V2, published on 26 Oct 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-2021-34586 in the wild and no public exploit code.

Affected product: CODESYS V2. 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-2021-34586/ (Markdown: https://insights.sbomify.com/CVE-2021-34586/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-34586
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-34586
- OSV: https://osv.dev/vulnerability/CVE-2021-34586

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-34586/
Summaries are generated and may contain mistakes; the official description above is the record.