This works by taking advantage of a format string exploit. It is by definition undefined behavior. It just so happens that this behavior is constant an gives th

This works by taking advantage of a format string exploit. It is by definition undefined behavior. It just so happens that this behavior is constant an gives the ability to change the flow of the program. At least in the popular glibc. However if someone were to rewrite how printf works but didn't allow the format string vulnerability, it would still be a valid c compiler.