This latest security hole influences the privacy of Facebook users who access Yelp. As you probably already know, Yelp is - alongside Docs.com and Pandora - a site that has partnered with the popular social network and has automatic access to a great portion of its users' data, in order to personalize their browsing experience.
The problem with this setup is that when such a site is compromised, the consequences can extend to Facebook and its users - as security consultant George Deglin can attest.
He discovered an exploit that would make it possible for a malicious site to harvest all the information that users have on their Facebook profile and is available for access from Yelp (email, name, current location, friend list, etc.). The exploit would be able to do this by using XSS to inject malicious code into Yelp.
As he explained to TechCrunch: "The script in my example would capture the browser cookies set for Yelp.com, extract a key required to make Open Graph API requests to the Facebook API, and send that key to my site. My site would then make a request for your name, email, etc. and store it in a database."
The most frightening thing about this is that the exploit could do it's thing even if you have never visited the Yelp website. But, luckily for all Facebook users, Deglin has never had any intention take advantage of this security hole and has notified Yelp and Facebook of it, which they proceeded to investigate and fix.