There is a few rumors floating around at the moment. Various sources are reporting that Iron Maiden are playing Bucharest, Romania and Graz, Austria in June as a part of the upcoming Maiden England European Tour 2013.

There are also reports that suggest the German festivals Rock Am Ring and Rock Im Park will announce the first names for the 2013 festivals tomorrow, Monday the 24th of September.
Maiden has previously headlined the festivals in 2003 and 2005. Considering that Maiden has played Wacken in both 2008 and 2010, it is likely that a return to the twin festivals is due next summer.