In iOS before 11.3, tvOS before 11.3, watchOS before 4.3, and macOS before High Sierra 10.13.4, an information disclosure issue existed in the transition of program state. This issue was addressed with improved state handling.
x18-leak iOS 11.2 introduced a kernel information leak that could be used to determine the kASLR slide. The issue was the result of a newly added feature, __ARM_KERNEL_PROTECT__, that inadvertently caused the address of the kernel function Lel0_synchronous_vector_64_long to appear in register x18 when obtaining the values of a thread's registers using thread_get_state. The