Yes, you are correct, it is UB. Try this code:

    void foo(const int * const p)
    {
        *(int*)p = 3; // UB? So sue me!
    }

It compiles with g++ and clang++ with no warnings or errors. gcc and clang, too. Sure, it's UB, but the compiler won't even warn you.

I.e. it serves no purpose, other than documentation. Let's try it in D:

    @safe
    void foo(const int *p)
    {
       *cast(int*)p = 3;
    }

    Error: cast from const(int*) to int* not allowed in safe code