How something has been stored is almost as important as how long it's been stored. If the packaging is intact, and it was stored in a cool, dark place, odds are that it will still rise just fine.
If you want to take some extra precautions to ensure a rise, there are two simple things that you can do:
- Add a little extra baking powder (not baking soda) to the mix. Maybe 1/4 to 1/2 tsp, as it's not really all that old.
- Add extra air. If it's a cake mix that calls for eggs, separate the eggs, whip the egg whites (in a clean, non-plastic bowl), and then fold that into everything else (that's already been mixed together).
You do risk ending up with a cake that might be a bit too light -- more chiffon / souffle like, rather than the standard texture.
You can also use the cake mix as an ingredient in other dishes. Besides the various 'dump cake' recipes out there, as it's mostly sugar and flour, you can add oatmeal and butter to it to make a streusel topping.
It's also worth noting that a 'flat cake' generally isn't that bad. Forgetting to add leavening to a chocolate cake was supposedly the origins of the brownie. Even the worst cake can be used as layers in a trifle, be dried and crumbled over ice cream or a parfait, or used to make a bread pudding (but avoid sugar in the custard so it's not overly sweet)