[gwillen]

I am not directly experienced with the threat involved. I know it is crossdomain-related; if you tell me it's cookies rather than JS, I'll believe you.

I have no idea whether Google normally sets document.domain, but I could certainly imagine it doing so; I feel like the "google.com" domain is one that any page under google.com is likely to believe it can trust, whether or not that trust is expressed programmatically. Certainly serving untrusted js anywhere under the google.com umbrella is likely to violate _someone_'s assumptions somewhere. I do not actually know it to be exploitable.

[Someone]

Why, then, did we get plus.google.com and not google+.com? (and aside: I find those (google.com) suffixes on HN that turn out to be links on plus.google.com confusing. For google.com URLs, I expect either search results or pages that represent google's position)