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Paypal Inc - Open Redirect Web Vulnerability
Paypal Inc - Open Redirect Web Vulnerability
Vulnerability Magazine: http://magazine.vulnerability-db.com/?q=articles/2015/09/11/paypal-inc-%C2%A0medium-severity-open-redirect-web-vulnerability-fixed
Vulnerability Laboratory ID (VL-ID):
Common Vulnerability Scoring System:
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 Research Team member Ayoub Ait Elmokhtar discovered an Open Redirect Web Vulnerability in the official PayPal Inc Web Application.
Vulnerability Disclosure Timeline:
2015-09-11: Public Disclosure (Vulnerability Laboratory)
PayPal Inc - Email Edg Service
Technical Details & Description:
The researcher started the research by the use of different versions of known redirect issues like for instance:
It will redirect you to evolution-sec.com since this is an open redirect vulnerability in Google, since Google allow open redirect and didn`t consider it in scope of Bug Bounty.
So appending this link url and visiting : email-edg.paypal.com/r/VTHX7UY/LP46GM/2OE8AOD/D9NJX6/74IKNJ/2V/h?a=https://www.google.com/search?btnI&q=allinurl:evolution-sec.com
It seems like it will redirect to evolution-sec.com but it won`t .. it will endup with a result which clearly appear to be a filter against Directory Filtering. This assumes that everything after www.domaine.com in this parameter won`t work. Well if we try accessing a subdomaine of google like http://XXX.google.com it will not work and the no redirection takes place.
So this is clearly appear to be some auth rules about redirect parameter rules :
1 - Subdomaine Filter
2 - Directory Filter
The final working POC which Bypass the Directory Filtering :
So this worked: email-edg.paypal.com/r/VTHX7UY/LP46GM/2OE8AOD/D9NJX6/74IKNJ/2V/h?a=https://www.google.com/search?btnI&q=allinurl://evil.com
This worked not: email-edg.paypal.com/r/VTHX7UY/LP46GM/2OE8AOD/D9NJX6/74IKNJ/2V/h?a=https://www.google.com/search?btnI&q=allinurl:evil.com
You should see the bypass with // which is likely an old python library URL rules bypass.
Oauth documentation say that you shouldn`t accept subdomaines neither directories in the redirect url which appear here as like this redirect URL.
Proof of Concept (PoC):
The vulnerability can be exploited by remote attackers without low privilege application user account and only low user interaction (click).
For security demonstration or to reproduce the vulnerability follow the provided information and steps below to continue.
Note: FINAL POC (does not work anylonger because the vulnerability has been patched by paypal.
The security risk of the open redirect web vulnerability in the paypal online service is estimated as medium. (CVSS 3.3)
The vulnerability is already patched by the paypal security team. The issue has been part of the official bug bounty program.
The researcher received a commercial reward for the bug bounty submission to the paypal security team.
Credits & Authors:
Ayoub Ait Elmokhtar (http://www.vulnerability-lab.com/show.php?user=Ayoub%20Ait%20Elmokhtar)
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