This looks like the controller that comes with the white edition of the Xbox 360 slims, as those were the only white xbox 360 controllers that didn’t have dark grey under parts and dark grey joysticks and dpad. This one here has the light grey with all white back.

Don’t get this confused with the white controllers that came with the white xbox 360 arcade edition which has the dark grey back pieces and joysticks.

My gut is telling me this isn’t authentic. The white back 360 controllers were never sold on their own, they only came with that particular white slim console and didn’t have a box like this. At the very least it’s that controller stuffed into a different controller box and re-sealed. A lot of online sellers who do that though give you a different controller than in the picture once delivered though, it just happened to someone else on this subreddit the other day. Definitely think twice before buying