Smalltalk is memory safe and dynamically type-safe. That is, you cannot invoke an inappropriate operation. You can try to do that, but the system will refuse to do so.
It's trivial to store sensitive data in a collection, for example, and then index it with the wrong index when trying to access and export adjacent non-sensitive data.
That's assuming you're mixing sensitive data and insensitive data in one collection. Heartbleed was access of random memory, a much more serious exploit