Directory Traversal is a vulnerability which allows attackers to access restricted directories and execute commands outside of the web server's root directory.
The following programs are vulnerable.
Programs that publish files using WEBrick::HTTPServer.new with the :DocumentRoot option
Programs that publish files using WEBrick::HTTPServlet::FileHandler
Affected systems are:
1. Systems that accept backslash (\) as a path separator, such as Windows.
2. Systems that use case insensitive file-systems such as NTFS on Windows, HFS on Mac OS X.
Your script should filter metacharacters from user input.