Skip to main content

Bounty leftover Part #1

One of the most important thing of anyone keen about security is to keep up to date with what is going on...
Hence I have a good collection of rss feed security's related.
One post that caught my attention a couple of months ago was this one from Stephen Sclafani. In a nutshell he was able to get a more than decent bounty of 20000$ exploiting some old Facebook API that is the precursor of Facebook's OAuth implementation.
Since I am a curious person I decided to give a look at these old APIs just to see the evolution of security over time. I was not hoping to find anything interesting under the bounty point of view since Stephen had found them all (he even did a second blog post collecting another 20000$!!).
Well, indeed I was right until some extent. I haven't found anything interesting under the security point of view (strictly speaking) nevertheless I was able to find a minor security issue (Information disclosure) that got rewarded by Facebook with a bounty... :)
Indeed http://api.facebook.com/restserver.php leaked some information about if a specific user has some application (https://developers.facebook.com/apps) installed or not.
Let's assume for example I would like to know if Mark Zuckerberg has some application installed or not. All I needed to know is the user id of Mark Zuckerberg and the app id.
Both those information are easily to get and kind of public.
The user id of Mark Zuckerberg is 4.
Now let's try to test if he has on of my application installed (Of course I would not have :)). The app id of my application is 213814055461514.
This information was easily reachable using the endpoint http://api.facebook.com/restserver.php.
To make a call an application makes a GET or POST request to the REST API endpoint:

POST https://api.facebook.com/restserver.php

method={METHOD}&api_key={API_KEY}&session_key={SESSION_KEY}&...&sig={SIGNATURE}

Now for our scenario we can ignore the parameter sig and focus on the session_key.
This is indeed (also, probably for backward compatibility) on the form -USER_ID

So If I tried to do

https://api.facebook.com/restserver.php?api_key=213814055461514&session_key=RANDOMDATA-4&method=bookmarks.get

I got back

<error_response xsi:schemaLocation="http://api.facebook.com/1.0/ http://api.facebook.com/1.0/facebook.xsd"><error_code>102</error_code><error_msg>The user has not authorized application 213814055461514.</error_msg><request_args list="true"><arg><key>api_key</key><value>213814055461514</value></arg><arg><key>session_key</key><value>RANDOMDATA-4</value></arg><arg><key>method</key><value>bookmarks.get</value></arg></request_args></error_response>


This of course proof the fact Mark Zuckenberg doesn't have this installed.
Let's see if I do have this installed (of course I do :)). My user id is 631367016.

So https://api.facebook.com/restserver.php?api_key=213814055461514&session_key=RANDOMDATA-631367016&method=bookmarks.get

result was

<error_response xsi:schemaLocation="http://api.facebook.com/1.0/ http://api.facebook.com/1.0/facebook.xsd"><error_code>102</error_code><error_msg>The session has been invalidated because the user has changed the password.</error_msg><request_args list="true"><arg><key>api_key</key><value>213814055461514</value></arg><arg><key>session_key</key><value>RANDOMDATA-631367016</value></arg><arg><key>method</key><value>bookmarks.get</value></arg></request_args></error_response>

So this tells me I have this application installed.
This worked for any user_Id / app_id combination.
Now as Egor Homakov showed sometime ago (using a different technique based on using Content-Security-Policy for evil) using 100-500 most popular Facebook clients we can build sort of user's fingerprint: what apps you authorize and what websites you frequently visit.As mentioned Facebook rewarded me for this and I am once more in the Facebook white hat page
Given the success of this I have decided to give a look to the way Google used to authorize applications on a pre-OAuth world and guess what ? :) I found an issue also there and Google also rewarded me. But I am afraid (since Google did not completely fix the issue) you have to wait for my next post Bounty leftover Part #2 :)

Comments

Popular posts from this blog

Slack SAML authentication bypass

tl;dr  I found a severe issue in the Slack's SAML implementation that allowed me to bypass the authentication. This has now been solved by Slack.
Introduction IMHO the rule #1 of any bug hunter (note I do not consider myself one of them since I do this really sporadically) is to have a good RSS feed list.  In the course of the last years I built a pretty decent one and I try to follow other security experts trying to "steal" some useful tricks. There are many experts in different fields of the security panorama and too many to quote them here (maybe another post). But one of the leading expert (that I follow) on SAML is by far Ioannis Kakavas. Indeed he was able in the last years to find serious vulnerability in the SAML implementation of Microsoft and Github. Usually I am more an "OAuth guy" but since both, SAML and OAuth, are nothing else that grandchildren of Kerberos learning SAML has been in my todo list for long time. The Github incident gave me the final…

Bug bounty left over (and rant) Part III (Google and Twitter)

tl;dr in this blog post I am going to talk about some bug bounty left over with a little rant.

Here you can find bug bounty left over part I and II
Here you can find bug bounty rant part I and II
Introduction In one of my previous post I was saying that: 

"The rule #1 of any bug hunter... is to have a good RSS feed list."
Well well well allow me in this post to state rule #2 (IMHO)

"The rule #2 of any bug hunter is to DO NOT be to fussy with 'food' specifically with left over"

aka even if the most experience bug hunter was there (and it definitely was my case here, given the fact we are talking about no one less than filedescriptor) do not assume that all the vulnerabilities have been found! So if you want some examples here we go.
Part I - GoogleI have the privilege to receive from time to time Google Vulnerability Research Grant. One of the last I received had many target options to choose from, but one in particular caught my attention, namely Google Issue T…

How to try to predict the output of Micali-Schnorr Generator (MS-DRBG) knowing the factorization

The article was modified since its publication. Last update was 09/10/2017 

See  also Part II and Part III of this series

tl;dr in this post we are going to describe how to try predict the output of Micali-Schnorr Generator (MS-DRBG)  knowing the factorization of the n value. If this sounds like, "why the hell should I care?", you might want to give a look at this great post from Matthew Green about the backdoor in Dual_EC_DRBG. But In a nutshell, quoting Matthew Green : Dual_EC_DRBG is not the only asymmetric random number generator in the ANSI and ISO standards (see at the bottom).   it’s not obvious from the public literature how one would attack the generator even if one knew the factorization of the n values above. What I am NOT claiming in this post though is that there is a backdoor in one of this standard.

Introduction
The first time I heard about this problem is about couple of weeks ago via this Matthew's tweet: As a curiosity, the NSA didn’t just standardize Dua…