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Paypal Inc Bug Bounty #30 - Filter Bypass & Persistent Vulnerabilities



Document Title:
===============
Paypal Inc Bug Bounty #30 - Filter Bypass & Persistent Vulnerabilities


References (Source):
====================
http://www.vulnerability-lab.com/get_content.php?id=705


Release Date:
=============
2014-09-26


Vulnerability Laboratory ID (VL-ID):
====================================
705


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.

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 Advisory Information:
==============================
The Vulnerability Laboratory Research Team discovered multiple web vulnerabilities in the official PayPal Here mobile notify me online service web-application.


Vulnerability Disclosure Timeline:
==================================
2014-09-26:	Public Disclosure (Vulnerability Laboratory)


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


Affected Product(s):
====================

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


Severity Level:
===============
Medium


Technical Details & Description:
================================
2 persistent POST Inject Vulnerabilities has been discovered in the official PayPal Here mobile Notify Me online service web-application.
The vulnerability allows remote attackers to inject own malicious script code on the application-side of the vulnerable web function.

The first 2 vulnerabilities are located in the `first_name` and `last_name` values of the `Notify Me` online service web-application. 
Remote attacker are able to inject own malicious script codes in the firstname and lastname values of the Notify Me send POST method request.
The execution of the injected script code occurs in the `biz.paypal` notify mail that arrives after the successful POST method request of the 
paypal api and web-application. The context execution is located in the mail header next to the introduction to the paypal customer.

A input filter validation bypass vulnerability has been discovered in the official PayPal Here mobile Notify Me online service web-application.
To inject the values the attacker needs to use a session tamper to interact. 

During the pentests the input fields disallows to insert of script codes (firstname & lastname). We tried to manipulate the POST request which 
is not connected to the input validation form (after a first load) with own malicious test values. The result was the successful execution of 
the malicious test code in the paypal notify me service mail. The protection of the input was not connected to the session request which results 
in a successful bypass by manipulation of the post values after the first web request.

The security risk of the persistent web vulnerability is estimated as medium with a cvss (common vulnerability scoring system) count of 3.5. 
Exploitation of the application-side web vulnerability requires no privileged web-application user account but low or medium user interaction.
Successful exploitation of the vulnerabilities result in persistent phishing mails, session hijacking, persistent external redirect to malicious 
sources and application-side manipulation of affected or connected module context.

Request Method(s):
				[+] POST

Vulnerable Module(s):
				[+] PayPal Here - Notify Me

Vulnerable Input Field(s):
				[+] Firstname
				[+] Lastname

Vulnerable Parameter(s):
				[+] first_name
				[+] last_name

Affected Module(s):
				[+] Notification Mail - You’re in line to get PayPal Here™


Proof of Concept (PoC):
=======================
The persistent vulnerability can be exploited by remote attackers without privileged application user account and with low or medium 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 application-side vulnerability ...

1. Open the paypal.com website and surf to the notify me service application site (https://www.paypal.com/webapps/mpp/credit-card-reader) 
2. Include your email and the random company name, firstname and lastname as regular (Do not save to notify yet!)
3. Start a session tamper to manipulate the request after the first attempt
4. Change the vulnerable firstname and lastname values with own script code payloads and continue to intercept the request
5. Open your mailbox and review the arrived paypal inc notify me service mail of the website formular
6. The persistent execution occurs in the header location next to the paypal customer introduction word `Dear [First-&Lastname]`
Note: The attacker is now able to manipulate the complete mail body and header of the notify me context to compromise other user accounts
7. Successful reproduce of the remote vulnerability!


PoC:  Notification Mail - Firstname & Lastname

<td style="font-family:verdana,sans-serif; font-size:13px; color:rgb(54, 54, 54); 
text-align:left; "><div class="mktEditable" id="copy"><p><br><span style="font-family: arial,helvetica,sans-serif; 
font-size: 12px;">Dear svenja "><[PERSISTENT INJECET SCRIPT CODE! FIRSTNAME & LASTNAME];)" <, <="" span=""></p>
<p><span style="font-family: arial,helvetica,sans-serif; font-size: 12px;">
Thank you for your interest in PayPal Here!  You are now a confirmed member of the PayPal Here “
Exclusive Release” wait list.
 PayPal Here will be available shortly and you will be notified with instructions on how to get your free mobile 
card reader and access to the app through iTunes or the Android Market (Play).</span></p>
<p><span style="font-family: arial,helvetica,sans-serif; font-size: 12px;">PayPal Here will make a big difference to your business.
 Instead of chasing payments or missing out on sales, you’ll be able to plug the card reader into your smart 
phone and get paid on the spot. </span></p>


--- PoC Session Logs [POST] ---
POST (Request): Standard
oid=00D300000000LaY
ret
URL=https%3A%2F%2Fwww.paypal.com%2Fwebapps%2Fmpp%2Fcredit-card-reader-thank-you
lead_source=Web-KNLBSTR
recordType=012800000003bgg
Campaign_ID=70180000000MGgf
email=bkm@xxxxxxxxxxxxxxxxx
first_name=Benjamin
last_name=KunzMejri
mobile=01776713371337
url=http%3A%2F%2Fwww.vulnerability-lab.com
company=vulnerabilitylab
Additional_Services__c=Android

POST (Request): Manipulated 
oid=00D300000000LaY
ret
URL=https%3A%2F%2Fwww.paypal.com%2Fwebapps%2Fmpp%2Fcredit-card-reader-thank-you
lead_source=Web-KNLBSTR
recordType=012800000003bgg
Campaign_ID=70180000000MGgf
email=bkm@xxxxxxxxxxxxxxxxx
first_name=<[PERSISTENT INJECTED SCRIPT CODE! #1]>
last_name="><[PERSISTENT INJECTED SCRIPT CODE! #1]< 
mobile=01776713371337
url=http%3A%2F%2Fwww.vulnerability-lab.com
company=vulnerabilitylab
Additional_Services__c=1337kungfu_0ne


Reference(s):
https://www.paypal.com/webapps/mpp/credit-card-reader
https%3A%2F%2Fwww.paypal.com%2Fwebapps%2Fmpp%2Fcredit-card-reader-thank-you


Solution - Fix & Patch:
=======================
The vulnerability can be patched by a secure encode and parse of the firstname and lastname values in the notify me POST method request.
Restrict the notify me input fields and disallow special chars. Parse the in the outgoing mail context the names that are stored in the 
dbms to prevent further script code executions. Connect a token to the session to prepare exceptions that prevent malicious interaction.


Security Risk:
==============
The security risk of the two persistent input validation vulnerabilities via POST method request are estimated as medium.
The security risk of the filter bypass vulnerability e in the paypal inc notify me form is estimated as medium.


Credits & Authors:
==================
Vulnerability Laboratory [Research Team] - Benjamin Kunz Mejri (bkm@xxxxxxxxxxxxxxxxx) [www.vulnerability-lab.com]


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