This will probably not lead to an exploit but:
Start Mario Kart 7 up and go to the bottom option which is Chaine Mario Kart (Mario Kart channel in English I think) and open it. Then press the back button. Now theres 2 options here:
Take out the game cart after like 2 seconds while it says something like " Please don't remove game cart or sd card" Then the game should still be running for like 1~2 seconds, then it will show an error like this (It's in French):
The other way is when you press back, it should say "Don't remove game cart or sd card", then you hold the power button down and press turn off. However, it looks like the 3ds is still writing to the SD card and the game cart. If you take the game cart out after you press turn off, it will ask you to go press the HOME button to go to the home menu. So, the system doesn't actually turn off until it's finished.
I speak and read French a little bit, but I don't know the language fluently.
Also now I can't connect online, and the game takes forever to turn off. When I go online, it just keeps saying "Connecting to server" or something and it never connects. Then when I suspend the software from the home menu, it takes about 5 min to close. Anybody know the issue here?