Happy DOM vulnerabilities

In versions before 20.0.2, it was found that --disallow-code-generation-from-strings is not sufficient for isolating untrusted JavaScript in happy-dom. The untrusted script and the rest of the application still run in the same Isolate/process, so attackers can deploy prototype pollution payloads to hijack important references like "process" in the example below, or to hijack control flow via flipping checks of undefined property. This vulnerability is due to an incomplete fix for CVE-2025-61927. The vulnerability is fixed in 20.0.2.

In Happy DOM library before version 20.8.9, there is a vulnerability where cookies are incorrectly attached when using fetch() with credentials: 'include'. Instead of cookies from the target URL, cookies from the current page origin (window.location) are attached, potentially leaking cookies from origin A to origin B.

A code injection vulnerability in Happy DOM versions 15.10.0 through 20.8.7 allows Remote Code Execution (RCE) by injecting arbitrary JavaScript expressions inside `export { }` declarations in ES module scripts. The `ECMAScriptModuleCompiler` directly interpolates unsanitized content into generated code, and the quote filter fails to strip backticks, enabling template literal-based payloads to bypass sanitization.