It's not official yet, nor do we know who's coming back to the Cubs, but it appears they have acquired righthander Dan Haren from the Marlins.
One beat writer from each team has tweeted this deal:
— Gordon Wittenmyer (@GDubCub) July 31, 2015
Haren is 34 and is on the last year of a contract that is apparently going to be paid by the Dodgers (who traded him to the Marlins over the winter), so there's not any financial risk to the Cubs other than a pro-rated portion of the minimum salary.