CVE-2014-10067
paypal-ipn before 3.0.0 uses the `test_ipn` parameter (which is set by the PayPal IPN simulator) to determine if it should use the production PayPal site or the sandbox. With a bit of time, an attacker could craft a request using the simulator that would fool any application which does not explicitly check for test_ipn in production.
Source: CVE-2014-10067