source: https://www.securityfocus.com/bid/2648/info

Perl Web Server, an experimental cross-platform web server project, does not prevent a remote user from requesting documents outside the ServerRoot (location of the virtual / directory).

This means that if an attacker knows the location of a sensitive file relative to the ServerRoot, he can retrieve the contents of the file by making an HTTP request containing the relative path. 

o retrieve /etc/password from a vulnerable host, request:

http://www.server.com/../../../../etc/passwd

The number of ../ path characters will depend on the ServerRoot (location of the virtual / directory) setting.