PayPal Session Fixation

`Document Title:  
===============  
PayPal Inc Bug Bounty #117 - Session Fixation Vulnerability  
  
  
References (Source):  
====================  
http://www.vulnerability-lab.com/get_content.php?id=1509  
  
EIBBP-31983 (P2)  
  
Video: http://www.vulnerability-lab.com/get_content.php?id=1615  
  
Vulnerability Magazine: http://magazine.vulnerability-db.com/?q=articles/2015/10/09/paypal-inc-bug-bounty-117-filter-bypass-remote-session-fixation-vulnerability  
  
  
Release Date:  
=============  
2015-10-09  
  
  
Vulnerability Laboratory ID (VL-ID):  
====================================  
1509  
  
  
Common Vulnerability Scoring System:  
====================================  
4.3  
  
  
Product & Service Introduction:  
===============================  
PayPal is a global e-commerce business allowing payments and money transfers to be made through the Internet. Online money   
transfers serve as electronic alternatives to paying with traditional paper methods, such as checks and money orders. Originally,   
a PayPal account could be funded with an electronic debit from a bank account or by a credit card at the payer s choice. But some   
time in 2010 or early 2011, PayPal began to require a verified bank account after the account holder exceeded a predetermined   
spending limit. After that point, PayPal will attempt to take funds for a purchase from funding sources according to a specified   
funding hierarchy. If you set one of the funding sources as Primary, it will default to that, within that level of the hierarchy   
(for example, if your credit card ending in 4567 is set as the Primary over 1234, it will still attempt to pay money out of your   
PayPal balance, before it attempts to charge your credit card). The funding hierarchy is a balance in the PayPal account; a   
PayPal credit account, PayPal Extras, PayPal SmartConnect, PayPal Extras Master Card or Bill Me Later (if selected as primary   
funding source) (It can bypass the Balance); a verified bank account; other funding sources, such as non-PayPal credit cards.  
The recipient of a PayPal transfer can either request a check from PayPal, establish their own PayPal deposit account or request   
a transfer to their bank account.  
  
PayPal is an acquirer, performing payment processing for online vendors, auction sites, and other commercial users, for which it   
charges a fee. It may also charge a fee for receiving money, proportional to the amount received. The fees depend on the currency   
used, the payment option used, the country of the sender, the country of the recipient, the amount sent and the recipient s account   
type. In addition, eBay purchases made by credit card through PayPal may incur extra fees if the buyer and seller use different currencies.  
  
(Copy of the Homepage: www.paypal.com) [http://en.wikipedia.org/wiki/PayPal]  
  
  
Abstract Advisory Information:  
==============================  
The Vulnerability Laboratory Core Research Team discovered a session fixation web Vulnerability in the official PayPal Inc (France) online service web-application.  
  
  
Vulnerability Disclosure Timeline:  
==================================  
2015-06-06: Researcher Notification & Coordination (Hadji Samir - Evolution Security GmbH)  
2015-06-08: Vendor Notification (PayPal Inc - Security & Bug Bounty Team)  
2015-07-04: Vendor Response/Feedback (PayPal Inc - Security & Bug Bounty Team)  
2015-09-30: Vendor Fix/Patch (PayPal Inc - Developer Team)  
2015-10-08: Security Reward (PayPal Inc - Bug Bounty Team) [3.000$]  
2015-10-09: Public Disclosure (Vulnerability Laboratory)  
  
  
Discovery Status:  
=================  
Published  
  
  
Affected Product(s):  
====================  
PayPal Inc  
Product: PayPal - Online Service Web Application 2015 Q2  
  
  
Exploitation Technique:  
=======================  
Remote  
  
  
Severity Level:  
===============  
Medium  
  
  
Technical Details & Description:  
================================  
A session fixation web vulnerability has been discovered in the official PayPal Inc online service web-application.   
The vulnerability allows remote attackers to manipulate user session information to takeover the data for malicious purpose.  
  
Data enters a web application through an untrusted source, most frequently an HTTP request. The data is included in an HTTP response   
header sent to a web user without being validated for malicious characters. HTTP response splitting is a means to an end, not an end   
in itself. At its root, the attack is straightforward: an attacker passes malicious data to a vulnerable application, and the application   
includes the data in an HTTP response header. To mount a successful exploit, the application must allow input that contains CR (carriage   
return, also given by %0d or /r) characters into the header AND the underlying platform must be vulnerable to the injection of such characters.   
These characters not only give attackers control of the remaining headers and body of the response the application intends to send, but also   
allow them to create additional responses entirely under their control. On the french paypal webpage for instance there is a vulnerability where   
an attacker can copy and overwrite a victims session ID and use the false ID to perform actions like session manipulation and cookie compromise.   
The vulnerability can be exploited by a successful manipulated GET method request through the France paypal online service web-application.  
  
The security risk of the unencrypted session fixation issue is estimated as medium with a cvss (common vulnerability scoring system) count of 4.3.   
Exploitation of the vulnerability requires no privilege web-application user account with low user interaction. Successful exploitation of the   
vulnerability results in manipulation of user session information and information disclosure.  
  
Request Method(s):  
[+] GET  
  
Vulnerable Module(s):  
[+] /cgi-bin/aao.com/   
  
Vulnerable Value(s):  
[+] error page (redirect 302)  
  
  
Proof of Concept (PoC):  
=======================  
The vulnerability can be exploited by attackers with restricted physical device access and without user interaction.   
For security demonstration or to reproduce the vulnerability follow the provided information and steps below to continue.  
  
String Bypass: %0d  
  
https://www.paypal.com/fr/cgi-bin///aao.com//%0dSet-Cookie:HaC80bwXscjqZ7KM6VOxULOB534=6RhGQapRfYgjamJv09KeTBVtJKw9oNcq8mnJDC_2H0t3denjeUdz8DnNpFn7iFUNVfPsPRu99_xUmvNcx_OaToy5En6pvysvcdCKmtdPawmYtupbEAVo4txChxNXlGdPmsWHB0; Domain=.paypal.com; Path=/;Expires=Mon, 08 Jun 2020 18:53:07 GMT; HttpOnly; Secure  
Note: https://www.paypal.com/fr/cgi-bin///aao.com// rerror page so will redirect to paypalproject.com > so any error page will redirect to paypalproject  
  
Reference(s):  
https://www.paypal.com/fr/cgi-bin/  
  
  
Solution - Fix & Patch:  
=======================  
2015-09-30: Vendor Fix/Patch (PayPal Inc - Developer Team)  
  
  
Security Risk:  
==============  
The security risk of the session fixation and filter bypass web vulnerability in the paypal framework is estimated as medium. (CVSS 4.3)  
  
  
Credits & Authors:  
==================  
Vulnerability Laboratory [Research Team] - Hadji Samir ([email protected]) [http://www.vulnerability-lab.com/show.php?user=Hadji%20Samir]  
  
  
Disclaimer & Information:  
=========================  
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