I'm not sure that you can have the moral high ground in a hypothetical scenario where Cuba conspires with Iran to attack the US. At that point both parties are banking on "might makes right".
Well, in this hypothetical scenario you can just as well say that Cuba is defending from the future threat from USA, the same way USA is now defending from future threat from Iran.
Not future threat though what US has put Cuba through the last 70 years any aggressive military from Cuba is probably justified. And no any attack from Cuba on US will still be morally ok if they attack US military and US banks etc.