No, UB has always been just undefined. `gets()`, one of the most exploited functions in the history of computers, does not require any clever malice from the compiler. And there are a lot of such examples. In fact practice has shown that it has always been very, very hard to write a program that cannot reach UB.
Thinking that you know what `undefined` really is results in undefined behavior.
Thinking that you know what `undefined` really is results in undefined behavior.