MWX Checksum Fixer
A command-line checksum fixer for Call of Duty: MW2 and Call of Duty: MW3 Savegame.svg files. Works on PC, Xbox 360, and PS3.
If you're looking for a tool for Call of Duty: Ghosts, it can be found at https://github.com/HunterStanton/Ghosts-Checksum-Fixer
If you're looking for a tool for Call of Duty: Infinite Warfare, it can be found at https://github.com/HunterStanton/IW-Checksum-Fixer
I have no idea about other Call of Duty games (such as Modern Warfare Remastered, Advanced Warfare, or Black Ops 1/2). Call of Duty 4 and 5 do not use checksummed saves.
MWXChecksumFixer.exe savegame.svg endian (big/little)
PS3 and XBox 360 use BIG endian. PC uses LITTLE endian.
After fixing, both the original and new checksums will be displayed for your reference.