# CVE-2021-39207: Deserialization of Untrusted Data in parlai

> Attackers can execute arbitrary code via unsafe YAML deserialization in the ParlAI framework, requiring users to upgrade or use SafeLoader.

- **Severity:** High 8.4 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 10 Sep 2021
- **Updated:** 4 Aug 2024

## What is CVE-2021-39207?

CVE-2021-39207 is a high-severity unsafe deserialization vulnerability in facebookresearch ParlAI, published on 10 Sep 2021. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

parlai is a framework for training and evaluating AI models on a variety of openly available dialogue datasets. In affected versions the package is vulnerable to YAML deserialization attack caused by unsafe loading which leads to Arbitary code execution. This security bug is patched by avoiding unsafe loader users should update to version above v1.1.0. If upgrading is not possible then users can change the Loader used to SafeLoader as a workaround. See commit 507d066ef432ea27d3e201da08009872a2f37725 for details.

Weakness: CWE-502 (Deserialization of Untrusted Data)

## Which versions are affected by CVE-2021-39207?

It affects 1 product.


Products: Facebook Parlai.

## How do I fix CVE-2021-39207?

Upgrade to a fixed version.

## Is CVE-2021-39207 being exploited?

There is no known exploitation of CVE-2021-39207 in the wild and no public exploit code.

## Other vulnerabilities in facebookresearch ParlAI

- [CVE-2021-24040](https://insights.sbomify.com/CVE-2021-24040/): Deserialization in ParlAI (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-39207 and fix it if it is affected.

What it is: CVE-2021-39207 is a high-severity unsafe deserialization vulnerability in facebookresearch ParlAI, published on 10 Sep 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-2021-39207 in the wild and no public exploit code.

Affected product: facebookresearch ParlAI. 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-2021-39207/ (Markdown: https://insights.sbomify.com/CVE-2021-39207/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-39207
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-39207
- OSV: https://osv.dev/vulnerability/CVE-2021-39207

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-39207/
Summaries are generated and may contain mistakes; the official description above is the record.