Full Path Disclosure

Overview

Full Path Disclose (AKA, FPD) vulnerabilities enable the attacker to see the path to the webroot/file. Eg: /home/omg/htdocs/file/. Certain vulnerabilities such as using the load_file() query to view page sources require the attacker to have the full path to the file they wish to view.

Severity

Low to Medium (circumstantial)

Exploit Likely-Hood

Extremely High

Examples

• Empty Array

If we have a site that uses a method of requesting a page like this:

http://site.com/index.php?page=about

We can use a method of opening and closing braces and causing the page to output an error. This method would look like this:

http://site.com/index.php?page[]=about

This renders the page defunct thus spitting out an error:

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

• Null Session Cookie

Another popular and very reliable method of producing errors containing a FPD is to give the page a nulled session using Javascript Injections. A simple injection using this method would look something like so:

javascript:void(document.cookie="PHPSESSID=");

By simply setting the PHPSESSID cookie to nothing (null) we get an error.

Warning: session_start() [function.session-start]: The session id contains illegal characters, 
valid characters are a-z, A-Z, 0-9 and '-,' in /home/example/public_html/includes/functions.php on line 2

Preventing

This vulnerability is prevented simply by turning error reporting off so your code does not spit out errors.

error_reporting(0);

Conclusion

It must be put across very clearly that this vulnerability in no way enables an attacker to gain full control of your website. However, this exploit often accompanies another, more serious one in which this will aid an attacker in controlling your website.