Leaking sensitive material is not unethical by definition, some situations might impose a moral imperative to act in this manner.

In the narrow ethical world of top down organizations, be they for profit corporations or the Army, it's of course a mortal sin, as is every other attempt to bring accountability to upper levels and redirect the flow of bullshit from top-down to bottom-up. I'll let you guess who decides what "ethics" stands for in this situation.