Federally illegal everywhere, including in state-legal states. But what actually happens at each TSA checkpoint varies wildly — some airports permit possession, some have amnesty boxes, and a few (on federal land) will charge you. Here's the policy for 24 major US airports.
Cannabis is a Schedule I controlled substance under federal law. Flying with it is a federal offense regardless of where you take off or land. State-legal possession on the ground does not give you the right to carry cannabis through TSA. Cabin crews and pilots cannot consume cannabis off-duty within FAA windows.