Information
A filename extension is a suffix added to a base filename that indicates the base filename's file format.
Rationale:
Visible filename extensions allows the user to identify the file type and the application it is associated with which leads to quick identification of misrepresented malicious files.
Impact:
The user of the system can open files of unknown or unexpected filetypes if the extension is not visible.
Solution
Perform the following to implement the prescribed state:
Select Finder
Select Preferences
Check Show all filename extensions
Alternatively, use the following command:
defaults write NSGlobalDomain AppleShowAllExtensions -bool true