While it's true that processor flaws destroy the assumptions that higher level components (such as any/all programming languages) build on, you don't need to go nearly that far to see unsafety in C++, even using only the most modern techniques: use-after-move of many types is undefined behaviour (for instance, dereferencing a std::unique_ptr that has been moved from), and iterator invalidation & dangling references aren't addressed by those smart pointers at all.