That doesn't sound right. C (and C++) permit you to do pointer arithmetic to derive a pointer value pointing to one element beyond the final element of an array. This special treatment doesn't extend to dereferencing though - if you deference that pointer, that's UB.

If you do pointer arithmetic to derive a pointer value pointing 2 or more elements beyond the final element of an array, that's undefined behaviour, even if you never dereference that pointer.