# CVE-2026-33943: Happy DOM ECMAScriptModuleCompiler: unsanitized export names are interpolated as executable code

> Attackers can achieve remote code execution by injecting malicious JavaScript into ES module export declarations processed by the Happy DOM library.

- **Severity:** High 8.8 (`CVSS:3.1/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:** Yes
- **Published:** 27 Mar 2026
- **Updated:** 15 Jul 2026
- **Also known as:** GHSA-6q6h-j7hj-3r64

## What is CVE-2026-33943?

CVE-2026-33943 is a high-severity code injection vulnerability in capricorn86 happy-dom, published on 27 Mar 2026. 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

Happy DOM is a JavaScript implementation of a web browser without its graphical user interface. In versions 15.10.0 through 20.8.7, a code injection vulnerability in `ECMAScriptModuleCompiler` allows an attacker to achieve Remote Code Execution (RCE) by injecting arbitrary JavaScript expressions inside `export { }` declarations in ES module scripts processed by happy-dom. The compiler directly interpolates unsanitized content into generated code as an executable expression, and the quote filter does not strip backticks, allowing template literal-based payloads to bypass sanitization. Version 20.8.8 fixes the issue.

Weakness: CWE-917 (Improper Neutralization of Special Elements used in an Expression Language Statement), CWE-94 (Improper Control of Generation of Code)

## Which versions are affected by CVE-2026-33943?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `happy-dom` | npm | From 15.10.0 | 20.8.8 |
| `happy-dom` | npm | From 15.10.0 | 20.8.8 |

Products: Capricorn86 Happy Dom.

## How do I fix CVE-2026-33943?

Upgrade happy-dom to 20.8.8 or later.

## Is CVE-2026-33943 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33943 exists.

## Other vulnerabilities in capricorn86 happy-dom

- [CVE-2026-34226](https://insights.sbomify.com/CVE-2026-34226/): Happy DOM's fetch credentials include uses page-origin cookies instead of target-origin cookies (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-33943 and fix it if it is affected.

What it is: CVE-2026-33943 is a high-severity code injection vulnerability in capricorn86 happy-dom, published on 27 Mar 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33943 exists.

Affected packages and fixed versions:
- happy-dom (npm): affected from 15.10.0; fixed in 20.8.8
- happy-dom (npm): affected from 15.10.0; fixed in 20.8.8

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-2026-33943/ (Markdown: https://insights.sbomify.com/CVE-2026-33943/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-33943
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-33943
- OSV: https://osv.dev/vulnerability/CVE-2026-33943

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-33943/
Summaries are generated and may contain mistakes; the official description above is the record.