OpenEMR before 8.4.0 Cross-Patient PHI Exfiltration via SMART Patient Launch

OpenEMR before 8.4.0 contains an authorization bypass allowing low-privileged SMART standalone-launch users to bind arbitrary patient UUIDs into the OAuth token context. Attackers with only the patients|demo ACL can select a victim during authorization and read that patient's clinical notes and documents through patient-scoped DocumentReference and Binary FHIR endpoints.