I understand the downside of this attack and what wrong can be done.
But I dont understand how is it done ?
Well, I need to educate myself, any pointers would be useful.
I suggest reading the paper. Section 3 (the section on cache injection) is clear and well-written.
In the grand scheme of things, I think this attack is of lesser severity. It requires the attacker to mount a MITM attack on you. It requires you to click through cert warnings. And if you do those two things, you're already in trouble anyway.
Best defenses: Try to avoid using open Wifi. Try to avoid clicking through cert errors. Certainly never click through cert errors when you are on open Wifi. If you want to be especially careful, set up a VPN and always use it any time you are on a third-party Wifi network.