According to the CISSP CBK Official Study Guide, a vulnerability in hardware would be the most difficult to detect. A vulnerability is a weakness or exposure in a system, network, or application, which may be exploited by threats and cause harm to the organization or its assets. A vulnerability can exist in various components of a system, network, or application, such as the kernel, the shared libraries, the hardware, or the system application. A vulnerability in hardware would be the most difficult to detect, as it may require physical access, specialized tools, or advanced skills to identify and measure the vulnerability. Hardware is the physical or tangible component of a system, network, or application that provides the basic functionality, performance, and support for the system, network, or application, such as the processor, memory, disk, or network card. Hardware may have vulnerabilities due to design flaws, manufacturing defects, configuration errors, or physical damage. A vulnerability in hardware may affect the security, reliability, or availability of the system, network, or application, such as causing data leakage, performance degradation, or system failure. A vulnerability in the kernel would not be the most difficult to detect, although it may be a difficult to detect. The kernel is the core or central component of a system, network, or application that provides the basic functionality, performance, and control for the system, network, or application, such as the operating system, the hypervisor, or the firmware. The kernel may have vulnerabilities due to design flaws, coding errors, configuration errors, or malicious modifications. A vulnerability in the kernel may affect the security, reliability, or availability of the system, network, or application, such as causing privilege escalation, system compromise, or system crash. A vulnerability in the kernel may be detected by using various tools, techniques, or methods, such as code analysis, vulnerability scanning, or penetration testing. A vulnerability in the shared libraries would not be the most difficult to detect, although it may be a difficult to detect. The shared libraries are the reusable or common components of a system, network, or application, that provide the functionality, performance, and compatibility for the system, network, or application, such as the dynamic link libraries, the application programming interfaces, or the frameworks.