Dangers of Remote Scripting

Came across this article recently: Dangers of Remote Scripting

This does raise an interesting problem that is hard to solve. Partnerships that involve running remote javascript are an important part of a lot of web sites. Its a powerful technology, allowing richer ads, content syndication, and outsourcing of page components, so business logic in javascript isn’t going to go away. It does increase your attack surface because a compromise of any of your partners can effect your site, as it did here.

You can’t really do any sort of validation in javascript, because the logic to do so would be out in the open and easily faked. I think a hybrid approach might be the best solution. Have your server do a “secret handshake” with the partner every so often, and if it fails then don’t display the script tag for their service. The handshake could go as far a cryptographic signing system that requires active support on the partner’s server, or it could be a passive system that checks for the existence of certain hidden urls and that the whois information hasn’t changed.

Any other ideas?