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PHP Security
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5. Outside file access
Normally, pages ending with .php will be handled forwarded to PHP by Apache and therefore the code will be hidden from the users. That the source code is hidden is one of the things that characterizes server-side scripting languages such as PHP. However, the PHP module or Apache might fail and the code might be displayed in plain unparsed text to the user. This is definitely not good. First of all, if the source is visible then it is much easier to find security issues in your application. Additionally, some scripts contain configuration files within the document root (the directory in which all files and sub-folders are publicly accessible from the outside world) and those will obviously not be parsed either thus presented to the user if they enter the filename into the URL. Personally I have experienced this before where I was on a small website and suddenly a misconfiguration of some sort displayed the source code to me. The website used a widely used application and I happened to know where the configuration file was. Sure enough, I was able to view that as well and from that I gathered the root password for the server (bad security practice to use the same password for multiple purposes and it is also bad security practice to use the root MySQL user). Being a nice person I did not do anything with it, but other people might not be as nice as I am and if you have the root password for a server then you can essentially do anything with it.
Another instance of this is the popular website Facebook which you have probably heard about in some way or another. What I explained before (server misconfiguration resulting in leaked source code) also has also happened to Facebook. Even big companies with people paid to configure the server apparently sometimes screws up and therefore it is necessary to take some security precautions in order to prevent source leakage if something like that should ever happen (something Facebook apparently did not).
It all has to do with how you layout your directory structure. So, all files within the document root can be retrieved by the user. Therefore we might as well move everything else out of there so people cannot directly access it. This means we might have index.php and some static files such as CSS, Javascript and images laying inside the document root. We can even take it further and do so the only thing that is in index.php is the following:
That particular snippet is the only thing the user will ever be able to see should something happen. So we might have a directory structure that looks like this:
/application
/controllers
/models
/views
/library
/public_html <-- document root
/index.php
/media
/images
/javascript
/css
/config
/cache
/tmp
/public_index.php
/logsBy laying out your files in this manner you will prevent that people will see things they are not supposed to see. It is easy to do so there is no reason why you would not.
