The Internet of Things (IoT) encompasses a network of physical objects embedded with sensors, software, and data processing technologies that can establish connections and exchange data with other devices and systems via the Internet. IoT devices are incorporated into various products, ranging from ordinary household items to complex industrial appliances. Despite the increasing demand for IoT, security concerns have impeded its development. This article systematically reviews IoT security research, focusing on vulnerabilities, challenges, technologies, and future directions. It surveys 171 recent publications in the field, providing a comprehensive discussion on the development status, challenges, and solutions in IoT. The article outlines IoT architecture patterns and typical features, evaluates existing limitations, and explores strategies for enhancing IoT security. Additionally, the article delves into known IoT attacks and discusses the security countermeasures and mechanisms to address these challenges. It explores the functional requirements of IoT security and explores related technologies and standards. Finally, the article discusses potential future research directions in IoT security.