Mario Kart 8 and Splatoon servers for the Wii U are coming back online tomorrow after they were taken offline due to security concerns earlier this year.
As posted on the official Nintendo website:
"In March 2023, Nintendo paused network services for the Wii U games Splatoon and Mario Kart 8 to address a vulnerability related to online play. The issue has now been fixed, and so we will resume online play for these games based on the schedule below. Please accept our sincere apologies for the extended waiting period."
It was theorized at the time as to the nature of the security concern, with Twitter User OatmealDome suggesting that the exploit could be related to something named ENLBufferPwn, and was an exploit that directly allowed users to take over the console of somebody who played online merely by implementing a few lines of code.
The fact that Nintendo has put the servers back online seemingly indicates that Nintendo has discovered the hole in their security and has managed to fix it, though there's no official confirmation from the company themselves on what this exploit was or how widespread the exploitation could possibly have been. With Mario Kart 8 currently playable on the Nintendo Switch and Splatoon 3 available on the same platform, it remains to be seen how many players will return to the older titles.