Undefined behavior is not always identifiable through static analysis. Obviously it can be checked against at runtime, but that's actually quite expensive. It would, for example, include bounds checks for everything, and overflow checks on all signed arithmetic.
That's not the worst of it: the truly intractable part is preventing use-after-free UB. The only ways to do this are (a) remove malloc from your language; (b) add a lifetime system (incompatible with all existing C libraries); (c) add a garbage collector (which most projects written in C will not accept for performance reasons).
I think that's mostly solved by changing the whole of the idea from "remove/disallow all undefined behavior" to "remove as much of the common needed undefined behavior as possible such that most programs need not really use it". Perfect is the enemy of good.
Are we arguing the same thing? If UAF is the cause of security problems, and UAF is undefined behavior now, redefining it under a special mode to mean "this is an error (whether or not the compiler enforces it)" at least clarifies the situation,and lets and included static analysis report an error as needed and capable.
That is, I'm not arguing that as much undefined behavior as possible should be made defined and possible, just that it's defined. That definition may very well be "you are not allowed to do this. Don't do this."
And once you've eliminated that, you have DoS bugs like forcing infinite loops, abandoned (referenced but unused) memory leaks, and worst-case hash table insertions. All of those are serious attacks for anything with a resource budget.
