custom-safe-themes is a variable defined in `custom.el'.
Its value is

  • This variable may be risky if used as a file-local variable.

Themes that are considered safe to load.
If the value is a list, each element should be either the SHA-256
hash of a safe theme file, or the symbol `default', which stands
for any theme in the built-in Emacs theme directory (a directory
named "themes" in `data-directory').

If the value is t, Emacs treats all themes as safe.

This variable cannot be set in a Custom theme.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 24.1 of Emacs.