Chances are the process has paused for user input, which means it will hang forever since cfexecute doesn’t expose an input stream for you to pipe any input. Try running the same process from the command line as the same user CF is to see what it does. It may be prompting for Git credentials.
For what it’s worth, there is also a Java library called JGit which has a java-based implementation of a Git client. I used it in CommandBox.