Performance-oriented way to protect files on PHP level?

Question

I am looking for some input on something I have been thinking about for a long time. It is a very general problem, maybe there are solutions out there I haven't thought of yet.

I have a PHP-based CMS.
For each page created in the CMS, the user can upload assets (Files to download, Images, etc.)

Those assets are stored in a directory, let's call it "/myproject/assets", on a per-page basis (1 subdirectory = 1 page, e.g. "/myproject/assets/page19283")

The user can "un-publish" (hide) pages in the CMS. When a page is hidden, and somebody tries to access it because they have memorized the URL or they come from Google or something, they get a "Not found" message.

However, the assets are still available. I want to protect those as well, so that when the user un-publishes a page, they can trust it is completely gone. (Very important on judicial troubles like court orders to take content down ... Things like that can happen).

The most obvious way is to store all assets in a secure directory (= not accessible by the web server), and use a PHP "front gate" that passes the files through after checking. When a project needs to be watertight this is the way I currently go, but I don't like it because the PHP interpreter runs for every tiny image, script, and stylesheet on the site. I would like have a faster way.

.htaccess protection (Deny from all or similar) is not perfect because the CMS is supposed to be portable and able to run in a shared environment. I would like it to even run on IIS and other web servers.

The best way I can think of right now is moving the particular page's asset directory to a secure location when it is un-published, and move it back when it's published. However, the admin user needs to be able to see the page even when it's un-published, so I would have to work around the fact that I have to serve those assets from the secure directory.

Can anybody think of a way that allows direct Apache access to the files (=no passing through a PHP script) but still controlling access using PHP? I can't.

I would also consider a simple .htaccess solution that is likely to run on most shared environments.

Answer 1

Anything sensitive should be stored in a secure area like you suggested.

if your website is located at /var/www/public_html

You put the assets outside the web accessible area in /var/www/assets PHP can call for a download or you can feed the files through PHP depending on your need.

If you kept the HTML in the CMS DB, that would leave only non-sensitive images & CSS.

If you absolutely have to turn on and off all access to all materials, I think your best bet might be symlinks. Keep -everything- in a non-web-accessible area, and sym link each folder of assets into the web area. This way, if you need to lock people out completely, just remove the symlink rather than removing all files.

I don't like it, but it is the only thing I can think of that fits your crtieria.

Answer 2

I'd just prevent hotlinking of any non-HTML file, so all the "assets" stuff is accessible only from the HTML page. Removing (or protecting) the page just removes everything without having to mess up the whole file system.

Answer 3

Use X-Sendfile

The best and most efficient way is using X-Sendfile. However, before using X-Sendfile you will need to install and configure it on your webserver.

The method on how to do this will depend on the web server you are using, so look up instructions for your specific server. It should only be a few steps to implement. Once implemented don't forget to restart your web server.

Once X-Sendfile has been installed, your PHP script will simply need to check for a logged in user and then supply the file. A very simple example using Sessions can be seen below:

session_start();

if (empty($_SESSION['user_id'])){
    exit;
}


$file = "/path/to/secret/file.zip";
$download_name = basename($file);

header("X-Sendfile: $file");
header("Content-type: application/octet-stream");
header('Content-Disposition: attachment; filename="' . $download_name . '"');

Important note:

If you are wanting to serve the file from another webpage such as an image src value you will need to make sure you sanitize your filename. You do not want anyone overriding your script and using ".." etc. to access any file on your system.

Therefore, if you have code that looks like this:

<img src="myscript.php?file=myfile.jpg">

Then you will want to do something like this:

session_start();

if (empty($_SESSION['user_id'])){
    exit;
}

$file = preg_replace('/[^-a-zA-Z0-9_\.]/', '', $_GET['file']);
$download_name = basename($file);

header("X-Sendfile: $file");
header("Content-type: application/octet-stream");
header('Content-Disposition: attachment; filename="' . $download_name . '"');