source: http://www.securityfocus.com/bid/1773/info

PHPix is a web-based photo-album system written in PHP. It is vulnerable to an attack that allows a malicious remote user to view arbitrary files on the target webserver with the privileges of the webserver. The problem is that "../" character sequences can be supplied by the user in an http variable that is used to reference a file on the webservers filesystem. As a result, the attacker can construct a path relative to the current working directory of the webserver using ".."'s and then the target filename/path to read any readable (to the uid of the httpd process) file on the filesystem. The information gained may make it easier to compromise the system in other ways.

Example:

http://target.com/Album/?mode=album&album=..%2F..%2F..%2F..%2F..%2F..%2F..%2F..%2Fetc&dispsize=640&start=0

The above line if given will output all the directories that are nested within /etc
directory. Other more sinister content can be revealed from there.