EXCEPTION_ACCESS_VIOLATION itself is well-defined and memory safe, but the program constructs that cause it are generally not. A use-after-free or null pointer

EXCEPTION_ACCESS_VIOLATION itself is well-defined and memory safe, but the program constructs that cause it are generally not. A use-after-free or null pointer dereference may cause an access violation in one run but corrupt memory and keep going in another. This is a very typical approach to building an exploit- find something like this and then tweak the input to turn it into something worse. This also plays into undefined behavior- unless the source language itself guarantees that a particular program will generate an access violation, chances are the access violation only happens by luck. For example, null pointer dereference is typically UB rather than specified as a crash, because while accessing the actual address 0 will reliably cause an access violation (assuming you are in such an environment), field projection and array indexing can move that address up out of the 0 page and lead to arbitrary memory access.