# CVE-2021-21249: Post-Auth Unsafe Yaml deserialization

> Authenticated attackers can achieve remote code execution in OneDev via unsafe YAML deserialization using SnakeYaml.

- **Severity:** Critical 9.6 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 15 Jan 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-7xhq-m2q9-6hpm

## What is CVE-2021-21249?

CVE-2021-21249 is a critical unsafe deserialization vulnerability in theonedev onedev, published on 15 Jan 2021. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

OneDev is an all-in-one devops platform. In OneDev before version 4.0.3, there is an issue involving YAML parsing which can lead to post-auth remote code execution. In order to parse and process YAML files, OneDev uses SnakeYaml which by default (when not using `SafeConstructor`) allows the instantiation of arbitrary classes. We can leverage that to run arbitrary code by instantiating classes such as `javax.script.ScriptEngineManager` and using `URLClassLoader` to load the script engine provider, resulting in the instantiation of a user controlled class. For a full example refer to the referenced GHSA. This issue was addressed in 4.0.3 by only allowing certain known classes to be deserialized

Weakness: CWE-502 (Deserialization of Untrusted Data), CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component)

## Which versions are affected by CVE-2021-21249?

It affects 1 product.


Products: Onedev Project Onedev.

## How do I fix CVE-2021-21249?

No fix has been published for CVE-2021-21249 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-21249 being exploited?

There is no known exploitation of CVE-2021-21249 in the wild and no public exploit code.

## Other vulnerabilities in theonedev onedev

- [CVE-2021-21242](https://insights.sbomify.com/CVE-2021-21242/): Pre-Auth Unsafe Deserialization on AttachmentUploadServet (critical 10.0)
- [CVE-2021-21243](https://insights.sbomify.com/CVE-2021-21243/): Pre-Auth Unsafe Deserialization on KubernetesResource (critical 10.0)
- [CVE-2021-21244](https://insights.sbomify.com/CVE-2021-21244/): Pre-Auth SSTI via Bean validation message tampering (critical 10.0)
- [CVE-2021-21245](https://insights.sbomify.com/CVE-2021-21245/): Pre-Auth Arbitrary File Upload (critical 10.0)
- [CVE-2022-39206](https://insights.sbomify.com/CVE-2022-39206/): CI/CD Docker Escape in OneDev (critical 9.9)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-21249 and fix it if it is affected.

What it is: CVE-2021-21249 is a critical unsafe deserialization vulnerability in theonedev onedev, published on 15 Jan 2021. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-21249 in the wild and no public exploit code.

Affected product: theonedev onedev. 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-2021-21249/ (Markdown: https://insights.sbomify.com/CVE-2021-21249/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21249
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21249
- OSV: https://osv.dev/vulnerability/CVE-2021-21249

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-21249/
Summaries are generated and may contain mistakes; the official description above is the record.