OpenEMR is a free and open source electronic health records and medical practice management application. Prior to version 8.0.0, in portal/portal_payment.php, the patient id used for the page is taken from the request ($pid = $_REQUEST['pid'] ?? $pid and $pid = ($_REQUEST['hidden_patient_code'] ?? null) > 0 ? $_REQUEST['hidden_patient_code'] : $pid) instead of being fixed to the authenticated portal user. The portal session already has a valid $pid for the logged-in patient.

Overwriting it with user-supplied values and using it without authorization allows a portal user to view and interact with another patient's demographics, invoices, and payment history-horizontal privilege escalation and IDOR. Version 8.0.0 contains a fix for the issue.