Depending on the operating system and distribution, the default configuration of Apache allows the indexing of directories. This enables search engines to index your file structure and possibly reveals sensitive data. The screenshot below shows an example of such data that can be retrieved with a simple HTTP request.
In this case only the list of extensions is revealed, but more
sensitive data can be found easily. The Apache configuration allows
you to enable or disable the indexing of directories by the
directive as shown in the following example:
<Directory /path/to/your/webroot/> Options Indexes FollowSymLinks </Directory>
By removing the
Indexes option, Apache does not show the list of
files and directories. Please note that the
Options directive can be
used in several containers (e.g.
<Location>, etc.). The correct configuration could look like the
<Directory /path/to/your/webroot/> Options FollowSymLinks </Directory>
If your specific website requires directory indexing at other places outside TYPO3, you should consider to deactivate this option in general but explicitly allow indexing for the required directories only.
Other web servers such as Microsoft Internet Services (IIS) allow similar configurations. See your web server's manual for further details on how to disable directory indexing.