[fulafel]

There's a specified Java memory model (JMM) and in the case the programmer shooting themself in the foot with concurrency by eg buggy synchronization, it provides just enough guarantees to protect the integrity of the state of the runtime itself.

(I didn't find this integirty of runtime specified in the JMM spec, hopefully it's in the other specs).

In the JMM terminology, the "you're in the clear" term is "well-formed execution". If you break the rules, you're not in "well-formed execution" land any more, and things may fly out of your orifices, but a specific type of C/C++ style dragon won't maybe fly out of your nose.

So there's a weak kind of memory safety, your app data in may still be garbled, possibly in an attacker-controlled way, but the attacker probably won't get remote code execution.