WP User Manager <= 2.9.18 - Missing Authorization to Authenticated (Subscriber+) Stripe Account Hijack via Stripe Connect Callback

The WP User Manager plugin for WordPress is vulnerable to unauthorized modification of data due to a missing capability check on the Connect::complete() function in versions up to, and including, 2.9.18. The function is registered on the admin_init hook (which fires for every authenticated user that reaches /wp-admin/, including Subscribers) and performs no current_user_can() or nonce verification before fetching Stripe credentials from the external WPUM connect service and writing them (publishable key, secret key, gateway mode, and connected Stripe account ID) into the wpum_settings option via wpum_update_option()/update_option(). This makes it possible for authenticated attackers, with Subscriber-level access and above, to hijack the site's Stripe integration by completing their own Stripe Connect OAuth flow and then invoking the callback on the target site, causing all subsequent Stripe payments to be routed to the attacker's Stripe account.