Wednesday, April 15, 2015

Google, Microsoft and token leaks

Some stir recently was caused by OAuth open redirector and even an RFC security addendum was created for it. While this was known for quite some time already, it's still good to remind the general public. So here's another known issue - an Open Redirector in OpenID.
It works like this - whenever "checkid_immediate" mode is used it redirects without any questions asked. And here's an example in
For a full exploit let's just use OAuth app (created by Google) that imports some data from Microsoft:
And here's the full Proof of Concept:
If you now inspect the URL, you'll notice that token was sent to my third party site.

And here the real problem with Authentication Providers comes in - is this a Relying Party (Google) or Authentication Provider (Microsoft) problem? Whatever the answer - users are the ones suffering.