Vendor: Patrick Breitenbach and Dave Nielsen [http://paypal.sf.net/]
Versions affected: PHP Toolkit for PayPal v0.50 (and may be prior)
Date: 12th January 2006
Type of Vulnerability: Sensitive Information Disclosure and Payment System
Bypass
Severity: Critical
Solution Status: Unpatched
Vendor was notified on 9th January 2006 without answer

Discovered by: .cens, uinC Team
Online location: http://www.uinc.ru/articles/vuln/ptpaypal050.shtml

Background:
>From vendor web-site:
"The PHP Toolkit provides a set of scripts that faciliatate the integration
of PayPal into an ecommerce service. It provides scripts that generate a
PayPal form dynamically as well as scripts to process Instant Payment
Notifications."

Description:
1) Payment System Bypass
If the payment through PayPal.com was completed successfully, payment data
is transferred to ipn.php, which in turn executes ipn_success.php, passing
it the parsed payment data as parameters using POST request. ipn_success.php
will enter the passed data straight into log file without verifying where
this data came from. This means, an attacker can reproduce the POST request
and enter the details of the successful payment into the log file even if
there was no payment through PayPal.com

2) Sensitive Information Disclosure
PHP Toolkit for PayPal vendor documentation recommends to set permissions
for the "logs" directory "../ipn/logs/" to 777. Data from ipn_success.php
suggests that the payment data log file is "logs/ipn_success.txt", which, if
installed according to documentation, will have global read permission. As a
result, anyone is able to view the transaction data.