This is not and exploit, just a really annoying glitch regarding the commendation for campaign ‘complete each level on legendary’. Completing this commendation grants you the ability to wear master chiefs armour online
I recently completed the whole campaign on solo legendary just to get the achievement(s) and I was also looking forward to showing off my new master chief armour online. To an extent, i was quite annoyed when i checked my campaign commendations and it said I had only completed certain amount of levels on legendary. I realised that this was due to the recent update for xbox and i declined at that time which disconnects you from XBL and I proceeded to complete about 3 levels of halo 4 on solo legendary (the last 3 and probably the hardest in the game). I didn’t receive any commendation completion for those levels. One would think that the commendation would be somehow linked to the achievement. The game also says that I have completed all levels on legendary on the console and on waypoint.
https://app.halowaypoint.com/en-au/Halo4/schmandog/campaign/
But i guess complaining isn’t going to do anything because i doubt 343i will fix this issue, so i may as well go and redo those missions again whilst connected to XBL.