Wall Street Journal
In a Web security context, these websites essentially allow arbitrary executable code, supplied by the third-party, complete access to the browser DOM and the user’s session information. *Exception being IMG SRC loads* That means they can hijack accounts by stealing authentication cookies; change the news or ask for passwords by altering what the user sees on the screen; redirect users to malware laden websites; force browsers to attack other systems, and more. By including Web widgets from an uncontrolled source on your pages, the third-party’s entire infrastructure must be included as part of the implicit trust model. These dangers have been previously discussed by Tom Stripling where the third-party service provider was assumed to be the potential nefarious source. I think the concern lies a bit deeper, where a malicious Web 2.0 pivot attack comes in.
If a bad guy, APT or a less-skilled adversary, wants to surreptitiously compromise a (relatively) hardened Web presence (or its users), they don’t necessarily need go after the target directly, they could instead go after the aforementioned third-party providers. How many of these third-parties take security as seriously as their customers do? Assumed few, but we really don’t know for certain. Please comment below is you have experiences here to share? How many organizations really check up on the third-party’s security posture or even know enough take this risk into consideration? Again, some do, but very few in my personal experience. The organization might dismiss the concern by saying something like:
"If X gets hacked we'll have bigger problems on our hands."
Important to add is that during a Web 2.0 pivot attack no traffic is directly seen by the primary target, which basically makes it impossible for them to detect/thwart the attack before a compromise. Post third-party compromise, it might be nearly as hard to detect a Web widget code update unless you can somehow monitor the content changes in unexpected ways. This of course assumes the primary target knows how, when, or if the third-party changes the code (rare). Not to mention the inclusion of Web page widgets is almost always beyond the visibility of a security team, because this process is largely managed through marketing / product management (not so much application development) and can easily happen at any time with zero notice.
Yes, the HTML 5 sandbox would be really nice to have.