# CVE-2021-24037: Use After Free in Hermes

> Attackers can execute arbitrary code via crafted JavaScript in Hermes if the application permits untrusted script evaluation.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/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:** Not needed
- **Fix available:** Yes
- **Published:** 15 Jun 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-mph8-6787-r8hw

## What is CVE-2021-24037?

CVE-2021-24037 is a critical use after free vulnerability in Facebook Hermes, published on 15 Jun 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A use after free in hermes, while emitting certain error messages, prior to commit d86e185e485b6330216dee8e854455c694e3a36e allows attackers to potentially execute arbitrary code via crafted JavaScript. Note that this is only exploitable if the application using Hermes permits evaluation of untrusted JavaScript. Hence, most React Native applications are not affected.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2021-24037?

2 open source packages ship an affected version, including hermes-engine. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `hermes-engine` | npm | All versions | 0.8.0 |
| `hermes-engine` | npm | All versions | 0.8.0 |

Products: Facebook Hermes.

## How do I fix CVE-2021-24037?

Upgrade hermes-engine to 0.8.0 or later.

## Is CVE-2021-24037 being exploited?

There is no known exploitation of CVE-2021-24037 in the wild and no public exploit code.

## Other vulnerabilities in Facebook Hermes

- [CVE-2023-23556](https://insights.sbomify.com/CVE-2023-23556/): Memory corruption in Hermes (critical 9.8)
- [CVE-2023-23557](https://insights.sbomify.com/CVE-2023-23557/): Memory corruption in Hermes (critical 9.8)
- [CVE-2023-25933](https://insights.sbomify.com/CVE-2023-25933/): Memory corruption in Hermes (critical 9.8)
- [CVE-2023-28081](https://insights.sbomify.com/CVE-2023-28081/): Use after free in Hermes (critical 9.8)
- [CVE-2023-30470](https://insights.sbomify.com/CVE-2023-30470/): Use after free in Hermes (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-24037 and fix it if it is affected.

What it is: CVE-2021-24037 is a critical use after free vulnerability in Facebook Hermes, published on 15 Jun 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-2021-24037 in the wild and no public exploit code.

Affected packages and fixed versions:
- hermes-engine (npm): affected all versions; fixed in 0.8.0
- hermes-engine (npm): affected all versions; fixed in 0.8.0

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-2021-24037/ (Markdown: https://insights.sbomify.com/CVE-2021-24037/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-24037
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-24037
- OSV: https://osv.dev/vulnerability/CVE-2021-24037

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-24037/
Summaries are generated and may contain mistakes; the official description above is the record.