Hi, my country application of cookies law calls for blocking all cookies (third part too) before they are accepted.

Probably not true. What country is this? In the UE directive, normal cookies like login cookies are allowed without annoying the users with stupid popups.

Until now I didn't find a free solution for b2evolution

There is a solution for b2evolution if you really want to annoy your users: activate the "EU cookie consent" that is included in the b2evolution package.

See: http://plugins.b2evolution.net/cookie-consent-plugin

Thank's you for your reply, I try EU cookie consent but is not enough in Italy. I have to block user downloading all third part cookies (you're right not all but all third part like social share buttons) before user takes any action.
EU cookies is only a banner but doesn't block anything.
Best regards

Again:

Cookies clearly exempt from consent according to the EU advisory body on data protection include:

• ...
• third‑party social plug‑in content‑sharing cookies, for logged‑in members of a social network.