Appointment Booking Plugin <= 5.7.1 - Insecure Direct Object Reference to Unauthenticated Unauthorized Transaction Intent Creation/Modification and Invoice Enumeration via 'invoice_id' Parameter

The Appointment Booking Plugin – LatePoint | Calendar & Scheduling for WordPress plugin for WordPress is vulnerable to Insecure Direct Object Reference in versions up to, and including, 5.7.1 via the OsPaypalConnectController::create_order_for_transaction() action registered as a public (unauthenticated) route through wp_ajax_nopriv_latepoint_route_call. The handler loads an OsInvoiceModel by a sequential integer 'invoice_id' with no access-key/UUID or ownership check (the sibling Stripe and Razorpay handlers require a 128-bit access-key UUID via OsInvoicesHelper::get_invoice_by_key), and then calls OsTransactionIntentHelper::create_or_update_transaction_intent() which persists a transaction intent tied to the target invoice's customer_id, order_id and charge_amount and regenerates its intent_key before the PayPal-configured guard is reached. This makes it possible for unauthenticated attackers to enumerate invoices belonging to arbitrary customers, create unauthorized transaction-intent rows linked to another customer's data, and overwrite the intent_key of any in-flight NEW-status transaction intent — invalidating the intent_key that legitimate Stripe/Razorpay flows are waiting on and breaking payment webhooks for those customers.