### Existing Surveys and Our Contributions
[64] explored the security challenges in IoT-Fog networks, emphasizing the vulnerabilities and attacks in the fog layer. They proposed a Blockchain and Fog-computing-enabled security service architecture, utilizing Hyperledger Fabric for fog nodes at the edge. The focus is on authentication, equipment-cloud channel privacy, and defense against malicious attacks. This work primarily addressed energy efficiency and hardware aspects of IoT and Blockchain integration, while our work takes a broader approach. We comprehensively analyze various security threats and vulnerabilities in IoT, offering a detailed attack taxonomy. Our proposed security solutions cover diverse layers, communication protocols, and network topologies, providing a holistic view of IoT security. The work of [PERSON] et al. [53] presented the attacks and the mitigation techniques related to the wireless infrastructures of IoT systems covering the most frequently used wireless communication technologies from the resource-constrained perspectives. The authors also provided a classification of the attacks based on a security-service-based attack. They also presented mitigation techniques of certain attacks, provided some guidelines to the user, and highlighted the limitation of these security measures. However, the complete security requirements of the IoT systems in different levels, such as operational level, information level, and access level, is not a part of the research. Similarly, the work of [PERSON] [54] focused on the security, privacy, and trust of mobile IoT (M-IoT) devices. The authors also discussed several available secure frameworks for M-IoT devices, such as an access control and authorization-based framework, risk-assessment-based framework, authentication-based framework, and secure services-based framework as a secure solution to tackle IoT vulnerabilities and attacks. In contrast, more rigorous classification of the attack surface and complete security of different level of the IoT network is not considered therein. [PERSON] et al. [55] aimed to present the prior works of edge-based security designs for IoT solutions. The authors also proposed an edge-centric IoT architecture. However, the other important aspects of the IoT systems attack surfaces, such as service vulnerabilities and cryptographic weaknesses, were not discussed. [PERSON] et al. [65] addressed the IoT security issues and probable counter measures from a more practical perspective. This article focused on four communication protocols mostly used in IoT devices, namely ZigBee, Bluetooth low energy (BLE), 6 LoWPAN, and LoRaWAN. However, a general layer-wise security solution was not discussed in that research. In this article, we present a holistic analysis of IoT security problems that includes a detailed discussion on the vulnerabilities and attack surface of the IoT network. We also provide a comprehensive attack taxonomy of the IoT attacks based on adversary and device properties, data privacy, and severity level. Moreover, the available effective techniques to secure the IoT solutions are also presented in this research. Furthermore, we also propose a Blockchain-based forensic framework to investigate and identify security issues of the IoT-based systems. Our specific contributions are highlighted as follows:  
1. We provide a comprehensive analysis of various security threats and vulnerabilities in IoT. Different from the existing surveys, this article identifies various attack surfaces and categorically discusses the associated vulnerabilities. We formulate an attack tree to classify the attacks in terms of their severity level and present a detailed attack taxonomy that encompasses a wide spectrum of how devices, hosts, access levels, locations, and strategies, among others, play a role in initiating respective attacks. 2. From a systems design perspective, we introduce the concept of a security landscape that can reflect multi-modal complexity based on applications, services, devices, and connectivity associated with an IoT system of interest.