I think I see your point - that despite the way C++ libraries can and do expose UB if not used as intended, it doesn't mean that Windows does the same.

For what it's worth, I read that POSIX does have UB in the spec (as in, distinct from how the compiler is allowed to break things in terms of language-level UB), at least in some ghastly signal handling situations. I wasn't able to find at a glance whether Windows does too, or if it categorically doesn't.

> According to POSIX, the behavior of a process is undefined after it ignores a SIGFPE, SIGILL, or SIGSEGV signal that was not generated by kill(2) or raise(3).