Tinypool: Prototype Pollution gadget in worker options leads to Remote Code Execution

`tinypool` passes worker options to `new Worker()` by reading them off a plain object whose prototype is `Object.prototype`. Options the application did not set are resolved through the prototype chain and then passed explicitly to `worker_threads.Worker`. Node core ignores `Worker` options inherited from `Object.prototype`. By reading them and passing them explicitly, tinypool re-materialises them as own properties and defeats that protection. Two keys reach code execution: 1. **`execArgv`** — polluting `Object.prototype.execArgv = ['--require', '/path/to/attacker.js']` causes every pool worker to load the attacker's script. 2. **`env`** — polluting `Object.prototype.env = { NODE_OPTIONS: '--require /path/to/attacker.js' }` achieves the same via environment injection. ## Root cause `dist/index.js` lines 508-511: ```js env: this.options.env, argv: this.options.argv, execArgv: this.options.execArgv, resourceLimits: this.options.resourceLimits, ``` `this.options` is built at line 470 via object spread: ```js this.options = { ...kDefaultOptions, ...options, filename, maxQueue: 0 }; ``` ## Impact Arbitrary code execution inside every worker the pool spawns, with the privileges of the host process. Because tinypool is the worker pool behind Vitest (~42M downloads/week), the natural blast radius is developer machines and CI runners — an attacker who lands a prototype-pollution primitive anywhere in the dependency tree gets code execution in the build/test pipeline, which is a suppl