The paper introduces the case study for attack surface analysis and monitoring with practical application of open-source intelligence (OSINT) methods. The case is based on the perimeters of healthcare organizations and aims to introduce the threat landscape of healthcare industry as well as methods to collect information about entry points and assets on network perimeter. Techniques and tools in this paper are not limited by organization type and can be applied for different network assets to prepare initial information during first stage of penetration testing and red team operations.