CVE-2026-33943: CAPRICORN86 Happy Dom

Critical severity, CVSS 9.8. EPSS: 1% chance of exploitation in the next 30 days.

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)

Published 2026-03-27. Last modified 2026-07-15.