[Thorrez]

>So without CORS, then someone might be able to create a landing page, which in the background triggers a `fetch` or `ajax` request to your bank's transaction endpoint. For 99.999% of people this wouldn't be effective because they are probably not a customer of this bank and are not logged in at the time of the request. But for some very tiny fraction of users, the browser would be tricked into populating the Cookie header from a previously created session in a different tab and would send this request.

Are you talking about an attack where the attacker tries to control the victim's bank account by initiating a transfer? That's a CSRF attack. CORS and the same origin policy don't prevent that attack by default. The browser will still send the request the request populating the cookie. The same origin policy will prevent the evil site from reading the response, not from making the request. To protect against this attack the bank needs to implement CSRF protection (e.g. checking the Origin header).