Maybe you found your answer already (but for everyone else).
This seems to be an issue on the server side of your settings.
Indexing (or directory browsing) is on by default.
Hence you'll see the directory by simply going to http://yourservername/admin/cli
I'm not sure how you access (or even have access to) the server side of your Moodle or how you host it.
But in Apache adding the following to httpd.conf and restarting the server should solve the issue:
Even if you're not using Apache the settings you need to apply should not differ that much.
Instead of seeing the contents you (and everybody else) will be met with a Forbidden error code when trying to enter http://yourservername/admin/cli
I hope this helps.