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Facebook Mobile Bug Bounty #7 - Redirect Vulnerability
From: Vulnerability Lab <research () vulnerability-lab com>
Date: Sat, 15 Jun 2013 13:19:59 +0100

Facebook Mobile Bug Bounty #7 - Redirect Vulnerability



Facebook Security ID: 159243257


Common Vulnerability Scoring System:

Facebook is an online social networking service, whose name stems from the colloquial name for the book given to 
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 
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 )

An independent Vulnerability Laboratory Researcher (Ismail Kaleem) discovered a open redirect web vulnerability in the 
Facebook Mobile web application.

2013-05-18:     Researcher Notification & Coordination (Ismail Kaleem)
2013-05-19:     Vendor Notification (Facebook Security Team - Bug Bounty Program)
2013-05-24:     Vendor Response/Feedback (Facebook Security Team)
2013-06-15:     Vendor Fix/Patch (Facebook Developer Team)
2013-06-16:     Public Disclosure (Vulnerability Laboratory)


Affected Products:
Product: Mobile Web Application (API) 2013 Q2



A unauthorized client side redirect web vulnerability is detected in the official Facebook Mobile web application 
The vulnerability allows remote attackers to redirect client side browser request over the portal to other unauthorized 
external target sites.

The vulnerability is located in the mobile application module when processing to request the appreg.php file with a 
manipulated `next` parameter via GET method.
Remote attackers can redirect customers by forming client site external requests with malicious links to an external 
source (urls).

Exploitation of the open redirect web vulnerability requires no facebook application user account but low or medium 
user interaction.
Successful exploitation results in open or unauthorized client side application redirects to malicious external targets 

Vulnerable Module(s):
[+] Facebook Mobile Application

Vulnerable File(s):
[+] appreg.php

Vulnerable Parameter(s):
[+] next

Proof of Concept:
The vulnerability can be exploited by remote attackers without privilege application user account and with low or 
medium user interaction.
For demonstration or reproduce ...

https://m.facebook.com/appreg.php?contactpoint=cashjun6%2540gmail.com&nonce=u62KkEhb&next=https://[CS GET REDIRECT WEB 

Note: There is no secure session hash and the cross domain is also not checked and protected.

The vulnerability can be patched by a secure restriction of the vulnerable parameter when processing to request 
unauthorized urls.

The security risk of the client side open redirect web vulnerability is estimated as low(+).

Ismail Kaleem - Senior Security Developer | IT Security Department
National Centre for Information Technology | Republic of Maldives

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