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.
The product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype.