Expected behavior

No undefined behavior in bitcoin's C++ code.

However, the Bitcoin code does contain UB in the net code in particular. All of the code that works with struct sockaddr needs to be inspected and fixed. For example here:

It is illegal/UB in C++ to do this type of aliasing and dereference a pointer that is reinterpre_casted in this way. C++ has stricter aliasing rules than C. For reference, see this: https://en.cppreference.com/w/cpp/language/reinterpret_cast#Type_aliasing

Suggested Fix

Use std::memcpy to copy the structs around and dereference them after copying them.