PayPal Inc Bug Bounty #117 - Session Fixation Vulnerability

From: Vulnerability Lab <>
Subject: PayPal Inc Bug Bounty #117 - Session Fixation Vulnerability

Document Title:
PayPal Inc Bug Bounty #117 - Session Fixation Vulnerability

References (Source):

EIBBP-31983  (P2)


Vulnerability Magazine:

Release Date:

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.

(Copy of the Homepage: []

Abstract Advisory Information:
The Vulnerability Laboratory Core Research Team discovered a session fixation web Vulnerability in the official PayPal Inc (France) online service web-application.

Vulnerability Disclosure Timeline:
2015-06-06: Researcher Notification & Coordination (Hadji Samir - Evolution Security GmbH)
2015-06-08: Vendor Notification (PayPal Inc - Security & Bug Bounty Team)
2015-07-04: Vendor Response/Feedback (PayPal Inc - Security & Bug Bounty Team)
2015-09-30: Vendor Fix/Patch (PayPal Inc - Developer Team)
2015-10-08: Security Reward (PayPal Inc - Bug Bounty Team) [3.000$]
2015-10-09: Public Disclosure (Vulnerability Laboratory)

Discovery Status:

Affected Product(s):
PayPal Inc
Product: PayPal - Online Service Web Application 2015 Q2

Exploitation Technique:

Severity Level:

Technical Details & Description:
A session fixation web vulnerability has been discovered in the official PayPal Inc online service web-application. 
The vulnerability allows remote attackers to manipulate user session information to takeover the data for malicious purpose.

Data enters a web application through an untrusted source, most frequently an HTTP request. The data is included in an HTTP response 
header sent to a web user without being validated for malicious characters. HTTP response splitting is a means to an end, not an end 
in itself. At its root, the attack is straightforward: an attacker passes malicious data to a vulnerable application, and the application 
includes the data in an HTTP response header. To mount a successful exploit, the application must allow input that contains CR (carriage 
return, also given by %0d or /r) characters into the header AND the underlying platform must be vulnerable to the injection of such characters. 
These characters not only give attackers control of the remaining headers and body of the response the application intends to send, but also 
allow them to create additional responses entirely under their control. On the french paypal webpage for instance there is a vulnerability where 
an attacker can copy and overwrite a victims session ID and use the false ID to perform actions like session manipulation and cookie compromise. 
The vulnerability can be exploited by a successful manipulated GET method request through the France paypal online service web-application.

The security risk of the unencrypted session fixation issue is estimated as medium with a cvss (common vulnerability scoring system) count of 4.3. 
Exploitation of the vulnerability requires no privilege web-application user account with low user interaction. Successful exploitation of the 
vulnerability results in manipulation of user session information and information disclosure.

Request Method(s):
                         [+] GET

Vulnerable Module(s):
                             [+] /cgi-bin/  

Vulnerable Value(s):
                              [+] error page (redirect 302)

Proof of Concept (PoC):
The vulnerability can be exploited by attackers with restricted physical device access and without user interaction. 
For security demonstration or to reproduce the vulnerability follow the provided information and steps below to continue.

String Bypass: %0d;; Path=/;Expires=Mon, 08 Jun 2020 18:53:07 GMT; HttpOnly; Secure
Note:    rerror page so will redirect to > so any error page will redirect to paypalproject


Solution - Fix & Patch:
2015-09-30: Vendor Fix/Patch (PayPal Inc - Developer Team)

Security Risk:
The security risk of the session fixation and filter bypass web vulnerability in the paypal framework is estimated as medium. (CVSS 4.3)

Credits & Authors:
Vulnerability Laboratory [Research Team] - Hadji Samir (  []

Disclaimer & Information:
The information provided in this advisory is provided as it is without any warranty. Vulnerability Lab disclaims all warranties, either expressed 
or implied, including the warranties of merchantability and capability for a particular purpose. Vulnerability-Lab or its suppliers are not liable 
in any case of damage, including direct, indirect, incidental, consequential loss of business profits or special damages, even if Vulnerability-Lab 
or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for 
consequential or incidental damages so the foregoing limitation may not apply. We do not approve or encourage anybody to break any vendor licenses, 
policies, deface websites, hack into databases or trade with fraud/stolen material.

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