Document Title:
===============
Facebook Bug Bounty #23 - Session ID & CSRF Vulnerability


References (Source):
====================
http://www.vulnerability-lab.com/get_content.php?id=1432

Facebook Security ID: 10202805822321483

Video: https://www.youtube.com/watch?v=SAr2AGLrBkQ

Vulnerability Magazine: http://magazine.vulnerability-db.com/?q=articles/2015/02/03/facebook-security-12500-bug-bounty-reward-security-researcher


Release Date:
=============
2015-02-03


Vulnerability Laboratory ID (VL-ID):
====================================
1432


Common Vulnerability Scoring System:
====================================
9.1


Product & Service Introduction:
===============================
Facebook is an online social networking service, whose name stems from the colloquial name for the book given to students 
at the start of the academic year by some university administrations in the United States to help students get to know 
each other. It was founded in February 2004 by Mark Zuckerberg with his college roommates and fellow Harvard University 
students Eduardo Saverin, Andrew McCollum, Dustin Moskovitz and Chris Hughes. The website`s membership was initially limited 
by the founders to Harvard students, but was expanded to other colleges in the Boston area, the Ivy League, and Stanford University. 
It gradually added support for students at various other universities before opening to high school students, and eventually to anyone 
aged 13 and over. Facebook now allows any users who declare themselves to be at least 13 years old to become registered users of the site.

Users must register before using the site, after which they may create a personal profile, add other users as friends, and exchange messages, 
including automatic notifications when they update their profile. Additionally, users may join common-interest user groups, organized by workplace, 
school or college, or other characteristics, and categorize their friends into lists such as `People From Work` or `Close Friends`. As of 
September 2012, Facebook has over one billion active users, of which 8.7% are fake. According to a May 2011 Consumer Reports survey, there are 
7.5 million children under 13 with accounts and 5 million under 10, violating the site`s terms of service.

In May 2005, Accel partners invested $12.7 million in Facebook, and Jim Breyer added $1 million of his own money to the pot. A January 2009 
Compete.com study ranked Facebook as the most used social networking service by worldwide monthly active users. Entertainment Weekly included the 
site on its end-of-the-decade `best-of` list, saying, `How on earth did we stalk our exes, remember our co-workers` birthdays, bug our friends, 
and play a rousing game of Scrabulous before Facebook?` Facebook eventually filed for an initial public offering on February 1, 2012, and was 
headquartered in Menlo Park, California. Facebook Inc. began selling stock to the public and trading on the NASDAQ on May 18, 2012. Based on its 
2012 income of USD 5.1 Billion, Facebook joined the Fortune 500 list for the first time, being placed at position of 462 on the list published in 2013.

(Copy of the Homepage: http://en.wikipedia.org/wiki/Facebook )


Abstract Advisory Information:
==============================
An independent Vulnerability Laboratory researcher discovered a session manipulation vulnerability and csrf bug in the official Facebook online service web-application.


Vulnerability Disclosure Timeline:
==================================
2015-02-03:  Public Disclosure (Vulnerability Laboratory)


Discovery Status:
=================
Published


Affected Product(s):
====================
Facebook
Product: Framework - Content Management System 2015 Q1


Exploitation Technique:
=======================
Remote


Severity Level:
===============
Critical


Technical Details & Description:
================================
A remote session validation vulnerability and cross site request forgery bug has been discovered in the official Facebook online service web-application.
The vulnerability allows to execute functions without secure validation to compromise user content in the online service web-application of facebook.

Th vulnerability is located in the comment id and legacy id of the comments function. Remote attackers with low privileged user accounts are able to delete 
postings of other users without auth. The attacker can intercept the session and exchanged the comment and legacy id to delete or add for example comments.
The issue is known as critical and impact a high risk to other user account. To manipulate the attacker needs to intercept the session to manipulate the 
legacy and comment ids.

The security risk of the session validation vulnerability and csrf issue is estimated as critical with a cvss (common vulnerability scoring system) count of 9.1. 
Exploitation of the vulnerability requires a low privileged application user account and no user interaction. Successful exploitation of the vulnerability results 
in unauthorized delete or add of user content in the comments function of facebook.

Vulnerable Module(s):
        [+] Comments

Vulnerable Parameter(s):
        [+] comment_id
        [+] legacy id


Proof of Concept (PoC):
=======================
The session manipulation vulnerability can be exploited by remote attackers with low privileged application user account and without user interaction.
For security demonstration or to reproduce the security vulnerability follow the provided information and steps below to continue.

Manual steps to reproduce the vulnerability ...

01. Login to your facebook account
02. Put a comment anywhere to a random post
03. Remove your comment by usage of the standard function in facebook
04. Capture the headers information on requesting to delete
05. Go to the victim account (any account not friend or there friends) because the issue works to both
06. Like his comment and capture the request by intercepting the values
07. Change your comment id with the victim comment id that you and change the legacy id
08. Replay the tampered request with the manipulated values
09. Now the comment will be unauthorized removed
10. Successful reproduce of the security vulnerability that allows to delete any comment of other users. thanks!


Solution - Fix & Patch:
=======================
The vulnerability has been patched due to the year 2014 by the facebook developer team. The issue was allowed to release in 2015 Q1.
The researcher received a reward amount of 12.500$ by the bug bounty program of the facebook whitehat team.


Security Risk:
==============
The security risk of the security vulnerability in the facebook framework is estimated as critical. (CVSS 9.1)


Credits & Authors:
==================
Joe Balhis (https://www.facebook.com/joe.balhis)


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=========================
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