What’s Vulnerable › Vulnerabilities

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

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-03-27 · updated 2026-10-26
• Weakness: CWE-94

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.

Affected products

• capricorn86 happy-dom: from 15.10.0 before 20.8.8 — fixed in 20.8.8

How to fix

Upgrade to a fixed version: capricorn86 happy-dom 20.8.8. Check the vendor advisory for mitigations.

References

• https://github.com/capricorn86/happy-dom/commit/5437fdf8f13adb9590f9f52616d9f69c3ee8db3c
• https://github.com/capricorn86/happy-dom/releases/tag/v20.8.8
• https://github.com/capricorn86/happy-dom/security/advisories/GHSA-6q6h-j7hj-3r64
• https://access.redhat.com/security/cve/CVE-2026-33943
• https://bugzilla.redhat.com/show_bug.cgi?id=2452522
• https://github.com/capricorn86/happy-dom/security/advisories/GHSA-6q6h-j7hj-3r64
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33943.json

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