If a server is making the proxied request, would this still matter? The server will pretend to be a legit browser submission?
In your link they mention reply. But what about a browser you control on the server?
Your browser connects to Google and tells the U2F token to auth using the www.google.com key: works
Your browser connects to [email protected] but no matter whether you believe that site to be Google, the U2F process means that it can only use a key for phish.me, which won't work on the Google.com servers even if they relay it.
The only attack which still works is if they control DNS and can forge an SSL certificate, at which point we have much bigger problems than phishing.
> The only attack which still works is if they control DNS and can forge an SSL certificate
Or if they're able to get some malware onto your system permitting them to change your dns servers or alter your hosts file, and add certificates to your OS/browser trust store.
Both of those fall into “control of DNS” or “forging an SSL certificate”. Besides, if they can do either of those things they don't need to phish you because they can just hijaack your existing browser when you login to the real site.
Sure, but that's raising the bar a hell of a lot higher than where it is currently, where all you need is a HTML email message that happens to superficially resemble something a random person might expect Google to send.
And in the long run I have more faith in making systems more secure via technological means than to try and convince users not to click on links in shady email messages. So by moving the problem into the technology domain and out of the social domain, I'd say it's a big win.
