# CVE-2021-21868: Deserialization in CODESYS

> An attacker can execute arbitrary commands by providing a specially crafted file to the CODESYS Development System due to unsafe deserialization.

- **Severity:** High 8.8 (`CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 18 Aug 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-j437-r3p6-wvg8

## What is CVE-2021-21868?

CVE-2021-21868 is a high-severity unsafe deserialization vulnerability in CODESYS, published on 18 Aug 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

An unsafe deserialization vulnerability exists in the ObjectManager.plugin Project.get_MissingTypes() functionality of CODESYS GmbH CODESYS Development System 3.5.16 and 3.5.17. A specially crafted file can lead to arbitrary command execution. An attacker can provide a malicious file to trigger this vulnerability.

Weakness: CWE-502 (Deserialization of Untrusted Data)

## Which versions are affected by CVE-2021-21868?

It affects 1 product.


Products: Codesys Codesys.

## How do I fix CVE-2021-21868?

No fix has been published for CVE-2021-21868 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-21868 being exploited?

There is no known exploitation of CVE-2021-21868 in the wild and no public exploit code.

## Other vulnerabilities in CODESYS

- [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-2019-13538](https://insights.sbomify.com/CVE-2019-13538/): Code injection in n/a (high 8.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-21868 and fix it if it is affected.

What it is: CVE-2021-21868 is a high-severity unsafe deserialization vulnerability in CODESYS, published on 18 Aug 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-21868 in the wild and no public exploit code.

Affected product: CODESYS. 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-2021-21868/ (Markdown: https://insights.sbomify.com/CVE-2021-21868/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21868
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21868
- OSV: https://osv.dev/vulnerability/CVE-2021-21868

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-21868/
Summaries are generated and may contain mistakes; the official description above is the record.