The quick growth of Internet of Things (IoT) devices has opened up tremendous possibilities for connectivity and innovation. However, because of their extensive use, cybercriminals frequently target these devices, primarily through zero-day assaults. These attacks take advantage of security vulnerabilities unknown to developers and, therefore, have no existing fixes or patches. As a result, they pose a significant threat. This article delves into the current landscape of zero-day attacks on IoT devices, examining how they work, the techniques used, their impact, and the strategies that can help mitigate them. In this review, we conducted a systematic analysis of current literature, threat reports, and industry case studies related to zero-day attacks in IoT devices. Our methodology involved collecting data from peer-reviewed journals, technical reports, and cybersecurity white papers to create a comprehensive taxonomy of vulnerabilities and exploitation techniques. This approach enabled us to identify emerging trends and gaps in current defense mechanisms, providing a holistic understanding of the challenges facing IoT security today. Our findings contribute to the field by offering actionable insights for researchers and practitioners. Specifically, we evaluate state-of-the-art countermeasures, highlight the potential of integrating advanced threat intelligence and AI-driven security solutions, and discuss the implications of emerging technologies such as quantum computing on future cybersecurity landscapes. These recommendations underscore the need for coordinated efforts among device manufacturers, cybersecurity experts, and regulatory bodies to enhance the resilience of IoT infrastructures against evolving cyber threats.