6.2 Turn on filename extensions

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 ensure file extensions are shown:
Graphical Method:

Open Finder

Select Finder in the Menu Bar

Select Preferences

Select Advanced

Set Show all filename extensions

Terminal Method:
Run the following command to enable displaying of file extensions:

$ sudo -u <username> defaults write /Users/<username>/Library/Preferences/.GlobalPreferences.plist AppleShowAllExtensions -bool true

example:

$ sudo -u seconduser defaults write /Users/secondname/Library/Preferences/.GlobalPreferences.plist AppleShowAllExtensions -bool true

See Also

https://workbench.cisecurity.org/files/3195

Item Details

Category: SYSTEM AND INFORMATION INTEGRITY

References: 800-53|SI-2(5), CSCv7|2.6

Plugin: Unix

Control ID: 72c50ed2f59d41dea61ccc5c3cd42162f45ec15b97ad6b8c992b5dffe2e1be84