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Paypal Bug Bounty #45 Bs - Remote Auth Bypass Session Vulnerability

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Posted 29 April 2013 - 02:28 PM

PayPal Bug Bounty #45 BS - Remote Auth Bypass Session Vulnerability



PayPal Security UID: og1eb1mgi

PayPal Inc Bug Bounty: 5000$


Common Vulnerability Scoring System:

Als spezialisierte Factoringgesellschaft für die Abwicklung von Rechnungskauf-Zahlungen im Internet wurde die BillSAFE GmbH 2008 
durch die Altgesellschafter der mediafinanz AG gegründet. Das Management der BillSAFE GmbH besteht ausnahmslos aus Risikomanagement-Experten 
mit jahrelanger Erfahrung aus der Betreuung von namhaften Online-Shops und Versandhandelsunternehmen. 

2009 erfolgte die reguläre Inbetriebnahme des Services mit der Anbindung der ersten 100 Online-Shops. 2010 beteiligte sich die eBay Tochter PayPal 
im Rahmen einer strategischen Partnerschaft an der BillSAFE GmbH. 2011 wurde ein neuer Unternehmensstandort auf dem eBay Campus in Berlin Dreilinden 
eröffnet, um die enge operative Zusammenarbeit mit PayPal weiter zu intensivieren. Seit Dezember 2011 ist die BillSAFE GmbH ein 100%iges PayPal 
Unternehmen und Teil der eBay Firmengruppe. Die von BillSAFE angebotenen Produkte bündeln die Erfahrung aus der Abwicklung von mehreren hundert 
Millionen E-Commerce Transaktionen durch PayPal mit der Expertise in der Bearbeitung von mehreren Millionen Inkassofällen durch die mediafinanz AG.

(Copy of the Vendor Homepage: )

The Vulnerabilitly Laboratory Research Team discovered a auth bypass vulnerability in Paypals Billsafe online payment service web application.

2013-01-27:    Researcher Notification & Coordination
2013-01-28:    Vendor Notification
2013-02-12:    Vendor Response/Feedback
2013-04-03:    Vendor Fix/Patch
2013-04-30:    Public Disclosure


Affected Products:
PayPal Inc
Product: BillSafe - Online Payment Service 2013 Q1



A auth bypass web session vulnerability is detected  in Paypals Billsafe online payment service web application.
The vulnerability typus allows an attacker to bypass the first login user session auth and change passwords and 
emails of billsafe web application accounts. 

The application is processing to request after a account activation plain passwords without any kind of token 
protection mechanism. The vulnerability is located in the first login section of the billsafe website when 
processing to load (after the activation) manipulated user/email/pass context. Remote attackers can manipulate 
accounts by live tampering the activation session link request. When the remote attacker is tampering the session 
live, he only needs to exchange the plain requested values (name/email/pass) with the earlier valid requested values.
After changing the vulnerable values the attacker only needs to send the same request again to reset 
any billsafe client application account.

Exploitation of the vulnerability requires no privileged application user account and no user interaction.
Successful exploitation of the vulnerability results in account compromise, account manipulation and account theaft.

Vulnerable Service(s):
                [+] PayPal Inc - BillSafe

Vulnerable Module(s):
                [+] Account - First Login

Vulnerable Parameter(s):
                [+] eMail
                [+] password 

Affected Module(s):
                [+] Account System

Proof of Concept:
The auth bypass vulnerability can be exploited by remote attackers without required user interaction or privileged application user account.
For demonstration or reproduce ...

                [+] Browser (Mozilla)
                [+] Tamper Data - Addon
                [+] A secound valid registration session change values

User-Agent=Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20100101 Firefox/17.0
Accept-Encoding=gzip, deflate
Cookie=__utma=22145316.759281629.1356643963.1356643963.1356653145.2; __utmc=22145316; 
PHPSESSID=mdkgkm8j91n4d57hdl8c9bjqo6; __utmb=22145316.96.9.1356654870355




Manually steps to reproduce ...
1. Start your web browser and open up the billsafe website
2. Register an user account via the main registration form
3. Go to your postbox and copy the link with the session
4. Open the browser, start tamper data and load the request (mail link) of the login register id
5. The tamper will show you the plain context which can be changed to your own values
6. Hold the request and change the values to your own new email account or password
7. Reload the page, change to your own new password, load the mail
8. Registration successful. You can now login with the account details of any other user.

2013-04-03:    Vendor Fix/Patch

The security risk of the auth bypass session web vulnerability is estimated as critical.

Vulnerability Laboratory [Research Team] - Benjamin Kunz Mejri (

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