This leak comes in the form of a photo posted to the brand new Infinite Warfare subreddit. It appears to be a reservation card from Target that depicts a special "Legacy Edition" of Call of Duty: Infinite Warfare, including a special remastered edition of Call of Duty: Modern Warfare. There isn't any indication as to when the game may be released on its own or if it's simply coming as a bundled item, but if it's true it's a safe bet we'll hear more by the time E3 rolls around.
It's a great thing to hear that Modern Warfare could very well be receiving a remastered edition, especially since it garnered so many fans. Aside from that, experiencing John "Soap" MacTavish's story once more without having to go back to an older console would be extremely convenient. This would be the latest addition to a long list of remastered games having been released as of late, including Resident Evil and System Shock: Enhanced Edition.
Update 4/29: Twitter account @charlieINTEL provides a clearer picture of the ad, which appears to be from a Canadian Target store. The original leaked image can be found below the tweet.