How could the Skype app log me out from my Facebook account on OSX? Isn't this a huge security flaw?

Question

According to this post (and to my personal experience), installing the Skype app on Facebook and the Skype client on OSX Mavericks will result in you being logged out from Facebook every time you launch the Skype client.

This question is not only to warn you of such an issue but to discuss what this could imply. It is my understanding that no third-party application should have arbitrarily access to navigation cookies: since this looks like what's happening, I'd like to know:

• How exactly can the Skype client trigger such a response?

• How is this not a security issue?

Answer 1

First off, I am not associated with Facebook in any way, shape or form and I have no idea how the site code actually works.

That said, this doesn't have to be a security issue at all. In very broad terms, here's how I suspect it's happening in the backend:

1. Somewhere in FB's vast, vast database of user info there is a table that basically lists "The connection with this session ID is signed on as this user."

2. When your skype app starts up and presents FB with your login credentials, Facebook notices that you are now connected with two different sessions, decides that something must have happened to your previous connection and clears it from the session table.

3. The next time that your web browser calls up a refresh of your facebook page as it's instructed to do via the ajax/jquery code on the facebook site, facebook no longer recognizes that particular session and asks you to log back in.

No security breaches, and the Skype app is blisfully unaware of the havoc it has wreaked.