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Showing posts from April, 2017

Meh : CSRF in Facebook Delegated Account Recovery

Note this is going to be a quick post.

This year, at Enigma 2017 Conference, Facebook introduced a way to move Account Recovery beyond Email and the "Secret" Question.
After the presentation the moved operationally and presented the first integration partner : Github.

These days I have seen a lot of press around this and both Facebook and Github open sourced their implementation and specification (also presented at F8).
Well it turned out that Facebook side was susceptible to Cross Site Request Forgery.
Really simple explanation:

The attacker start the integration with Github and stop the flow at the right moment. The create an attacker page as
<img src="…

CSRF in Facebook/Dropbox - "Mallory added a file using Dropbox"

tl;dr  Facebook Groups offers the option to upload files directly from the Dropbox account. This integration is done using the OAuth 2.0 protocol and suffered from a variant of the classic OAuth CSRF (defined by Egor Homakov as the the Most Common OAuth2 Vulnerability),  see video below:

Introduction  Facebook Groups offers the option to upload files directly from the Dropbox account:

This will allow to surf via browser the Dropbox account 

and post a specific file to the group.  This integration is done using a variant of the OAuth 2.0 protocol seen in this blog many many times. But once more, OAuth is an access delegation protocol standardized under the IETF umbrella. A typical OAuth flow would look like:
Usually the client initiates the OAuth flow in the following way:

then after that the resource owner has authorized the client the authorization server redirects the resource owner back to the client with an authorization code:
Then the OAuth dance continues....
Facebook/Dropbox i…