A flaw in Node.js HTTP request handling causes an uncaught TypeError when a request is received with a header named __proto__ and the application accesses req.headersDistinct. When this occurs, dest["__proto__"] resolves to Object.prototype rather than undefined, causing .push() to be called on a non-array. This exception is thrown synchronously inside a property getter and cannot be intercepted by error event listeners, meaning it cannot be handled without wrapping every req.headersDistinct access in a try/catch. This vulnerability affects all Node.js HTTP servers on 20.x, 22.x, 24.x, and v25.x