Full Path Disclosure Tutorial

Greetings from, well, me? :P

In this little write up today, I am going to try and explain you what 'FPD' is, how to detect it, analyze it, and some pretty good methods of finding it in the wild.

/* Note that my write up was intended to PHP-based websites, but some of the methods works for ASP/ASPX too. */
/* I never imply myself to be an expert. If you see any mistakes - You know what to do! */

But first... The hell is FPD?

'FPD' (Stands for Full Path Disclosure) is one of the most common methods of attacks (While I doubt this kind of action categorized as a form of an attack, it is still a highly-related method of website security testing), that Pen-testers / Hackers / whatever use in order to gain an error which will expose the full installation path of the targeted site. 

Why is this happening?

By default (Don't quote me here. Some web-services and packages disable this function, but partly in most cases), the PHP error reporting function -

Code:

error_reporting(0);

'1' = On. ==> 0 = Off.
Any kind of PHP error that happens when you load up a page will display itself on the page. That error is meant to notify the programmer about a coding glitch on his page.

The common error would basically look something similar to this -

Code:

Warning: function(function.name) [Function_name]: Some brief summery in /home/user-name/public_html/website.pony/rawr.php on line 126

The regular programmer would take in account everything, expect the full path, which does not interest him that much (Aside from the file name itself)... Unlike the intruder.

Now the question is: Why is the path needed?

Because, it is a must-have detail at some cases of those three attacks:

SQL Injection using load_file() & outfile

Those two SQL Queries (Also the 'dumpfile' query, so make it three) require the full path of the targeted directory in order to execute themselves.
Example:

Code:

/**/load_file('/home/pony/www/httpdocs/public_html/index.php')--
/**/into outfile '/home/pony/www/httpdocs/public_html/rawr.txt'--

Local File Inclusion (LFI)

Some variants of LFI attacks won't allow you to poison logs / use filters, so you can try loading your own way through the site. 

Symbolic linking (Symlinking) 

At some cases, when uploading a shell is not an option, you'd rather know the path in order to work a symbolic link - A shortcut.

And more methods which I can't come up with as for this moment.

So, How to cause it?

Oh, there's quite a few methods:

 Transforming X type of variables to type Y

Code:

?err=4 ==> ?err=lol

Let's say 'err' is a number-y variable. It means, it could only $_GET numbers to it's related code.
Sooo... Try to insert a string instead. Might work.

 Using false file names

Code:

?page=index.php ==> ?err=ThisDoesNotExist.php

Possible Output:

Code:

Warning: require(ThisDoesNotExist.php) [function.require]: failed to open stream: No such file or directory in /home/content/g/a/r/gardenlover/html/admin/index.php on line 25

Fatal error: require() [function.require]: Failed opening required 'ThisDoesNotExist.php' (include_path='.:/usr/local/php5/lib/php') in /home/content/g/a/r/gardenlover/html/admin/index.php on line 25

The script is including every kind name that goes through the $_GET, and prints the file under the requested name. Now, what will happen if we include a non-existing file?~

 Basically messing around with the value of the parameter

Code:

?err=4 ==> ?err=4.1
?err=4 ==> ?err=-4
?err=4 ==> ?err=4!

Sometimes, the value will be limited to only one style of inputs, and any kind of tweak would result a "Divided By Zero" PHP error.

 braces.

Code:

?err=4 ==> ?err[]=4

Well, it is messing up the parameter in a different way, so it's a different method xD
I believe this has something to do with the whole array usage at PHP (Uses braces?), not sure though.
Possible output:

Code:

Warning: opendir(Array): failed to open dir: No such file or directory in /home/omg/htdocs/index.php on line 84
Warning: pg_num_rows(): supplied argument ... in /usr/home/example/html/pie/index.php on line 131

 Messing around with the COOKIEZ

Code:

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