Accept Donations with PayPal < 1.5.3 - Unauthenticated Open Redirect

Description

The Accept Donations with PayPal & Stripe plugin for WordPress is vulnerable to Open Redirect in all versions up to, and including, 1.5.2. This is due to insufficient validation on the redirect url supplied. This makes it possible for unauthenticated attackers to redirect users to potentially malicious sites if they can successfully trick them into performing an action.