Divi Membership <= 2.3.0 - Unauthenticated Authentication Bypass via 'paypal_param' Parameter

The Divi Membership plugin for WordPress is vulnerable to Authentication Bypass in all versions up to, and including, 2.3.0. The `process_paypal_callback` function, hooked to the `init` action, accepts a base64-encoded `paypal_param` GET parameter with no IPN validation, no cryptographic signature check, no ownership verification, and no nonce, allowing it to trust an entirely attacker-controlled user ID value that is passed directly to `wp_set_current_user()` and `wp_set_auth_cookie()`. This makes it possible for unauthenticated attackers to log in as any existing WordPress user — including administrators — by supplying an arbitrary user ID in the `paypal_param` GET parameter, resulting in full site takeover. The vulnerability is further compounded by the fact that the PayPal gateway class is instantiated unconditionally regardless of whether PayPal is enabled or configured, ensuring the vulnerable hook is always registered on every front-end request.

This one needs no account at all, which puts it outside what login hardening can reach; WordSec's login security narrows the account-level paths around it, and the firewall is what inspects the request itself. None of that substitutes for the fix: Divi Membership 3.0.0 closes this, and updating the plugin is the step that ends it.

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