This is the first working save game hack/mod released for Modern Warfare 3. It has been released publicly by ‘coder123′ to all credit to him for his work.
This mod will give you unlimited ammo and the super jump ability along with a low gravity mod.
Download from the following link, change ID and start the game as normal. Remember to backup your original save game incase something goes wrong and you cant revert back.
This hack is for campaign mode only at this time. More information can be found in the developers forum.