Pages making GET requests across domains is so common and necessary that several technology standards would have to come together to propose a real fix. Every image or script loaded from a CDN. Anyone hosting their own static assets domains. Anyone using a plugin from Google, Facebook, Twitter, Disqus uses this ability.
The tech companies can't even easily create a system to whitelist sites allowed to embed them, because that would severely limit third party's ability to use their services freely and would introduce a huge performance bottleneck.
I haven't seen any particularly compelling solution to solving this. Things only guarded behind a GET request can be loaded by script, link, embed, object, img and iframe tags, and all of those have legitimate reasons for loading resources cross domain without requesting permissions for each one from the user.
What I don't get is how arbitrary cross-site POSTs with malicious values are allowed. As far as I can tell, anyone can post this form:
<form action="http://bank.com/send_money><input name="to_account" value="SCAMMER-1234"></form>
Worse, one article will tell you to only allow Referrer == "bank.com", and then another will tell you that even that is no longer enough?!!!
Why can't we change the browser or the web server layer to prevent this by default?!
So, in the context of this discussion, why don't the browsers make X-Frame-Origin: DENY the default behavior?????
It's user input. Don't trust user input.
I browser cannot do this. The OP probably saw some exploit code in an ad which was served in an IFrame, but the same-domain security model will not allow you to interact with another window or IFrame that is of a different domain.
Here's my take away from every CSRF article:
A malicious site will load your site in an iframe, fill in your form and post it. Fixing it requires some a token in your form, but I can see you don't understand how an extra hidden field in your form will make a difference so you're clearly not going to handle it correctly. You're screwed. Go home.
As far as I can tell, CSRF should have existed since javascript & frames. How have the browser vendors not fixed such a huge insecure-by-design flaw?