PayPal Community Forum Cross Site Scripting

`Title:  
======  
Paypal Bug Bounty #27 - Community Web Vulnerability  
  
  
Date:  
=====  
2012-11-24  
  
  
References:  
===========  
http://www.vulnerability-lab.com/get_content.php?id=704  
  
  
VL-ID:  
=====  
704  
  
  
Common Vulnerability Scoring System:  
====================================  
2.1  
  
  
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.  
  
On October 3, 2002, PayPal became a wholly owned subsidiary of eBay. Its corporate headquarters are in San Jose, California, United   
States at eBay s North First Street satellite office campus. The company also has significant operations in Omaha, Nebraska, Scottsdale,   
Arizona, and Austin, Texas, in the United States, Chennai, Dublin, Kleinmachnow (near Berlin) and Tel Aviv. As of July 2007, across   
Europe, PayPal also operates as a Luxembourg-based bank.  
  
On March 17, 2010, PayPal entered into an agreement with China UnionPay (CUP), China s bankcard association, to allow Chinese consumers   
to use PayPal to shop online.PayPal is planning to expand its workforce in Asia to 2,000 by the end of the year 2010.  
Between December 4ñ9, 2010, PayPal services were attacked in a series of denial-of-service attacks organized by Anonymous in retaliation   
for PayPal s decision to freeze the account of WikiLeaks citing terms of use violations over the publication of leaked US diplomatic cables.  
  
(Copy of the Homepage: www.paypal.com) [http://en.wikipedia.org/wiki/PayPal]  
  
  
Abstract:  
=========  
The Vulnerability Laboratory Research Team discovered a a client side Web Vulnerability and a stable error in the official Paypal Community Forum Portal.  
  
  
Report-Timeline:  
================  
2012-09-17: Researcher Notification & Coordination  
2012-09-18: Vendor Notification  
2012-10-19: Vendor Response/Feedback  
2012-10-29: Vendor Fix/Patch  
2012-11-26: Public Disclosure  
  
  
Status:  
========  
Published  
  
  
Exploitation-Technique:  
=======================  
Remote  
  
  
Severity:  
=========  
Medium  
  
  
Details:  
========  
A client side input validation vulnerability and a stable persistent error are detected in the official PayPal Community website.  
The vulnerability is located in the add tags function and the bound replace module.attackers can produce posts with permanent   
errors bye replacing a standard value string with > `` < ../ and a string code or path to an existing url. Normally it should not be   
possible to inject script code as foldername and replace it with more script code to crash with an unhandled exception. Attackers   
can inject on client side when the exception-handling is bypassed via another validation vulnerability.  
  
  
Vulnerable Module(s):  
[+] add tags  
  
Vulnerable Parameter(s):  
[+] rc  
  
  
Proof of Concept:  
=================  
The vulnerability can be exploited by remote attackers with medium or high required user inter action.  
For demonstration or reproduce ...  
  
  
POC:  
https://www.paypal-community.com/t5/forums/tagreplacepage/message-scope/core-node/board-id/US-Hot-Topics/user-scope/single/  
user-id/4716070/tag-scope/single/tag-id/rc=a%20onload=alert%28%22VL%22%29%20%3C%20%22%3E%3Ciframe%20src=a  
%20onload=alert%28%22VL%22%29%20%3Cc%20%22%3E%3C  
iframe%20src=a%20onload=alert%28%22VL%22%29%20%3C%20%22%3E%3Ciframe%20src=a%20onload=alert%28%22VL  
%22%29%20%3C/timerange/all/tag-visibility-scope/public  
  
--- Error Logs ---  
An Unexpected Error has occurred.  
Sorry, your request failed. A notification has been sent to the development team for investigation.  
Exception ID: 724C64A6  
Please click the Back button on your browser.  
  
Return to my original page  
  
ID: 724C64A6  
Session Time: 15:30 - 15:51  
  
Reference(s):  
../US-Hot-Topics.htm  
../public.html  
../all.htm  
../424675.htm  
  
  
Note:  
The bug exists but the exception-handling prevents the client side execution with a unhandled error and opened   
automatically a ticket for the dev team. It is very dangerous to allow special chars like > " < / ' - in the url   
itself because it results in multiple different errors after a while like you can see on the not sanitized calculated output.  
  
  
Solution:  
=========  
The vulnerability and stable error can be patched by parsing the rc parameter request.  
It also required to restrict the add tag function with a character mask, own exception-handling or filter.  
The result is the url with not anymore stable contain manipulate script code which results in permanent errors or client side script code attacks.  
  
2012-10-29: Vendor Fix/Patch  
  
  
Risk:  
=====  
The security risk of the non persistent input validation web vulnerability is estimated as low(+)|(-)medium.  
  
  
Credits:  
========  
Vulnerability Laboratory [Research Team] - Benjamin Kunz Mejri ([email protected])  
  
  
Disclaimer:  
===========  
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