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From: "Hugh Mann" <hughmann () hotmail com>
Date: Tue, 23 Mar 2004 07:13:29 +0000

Advisory Name: ALLO ALLO WS_FTP Server
Impact       : Arbitrary code execution as SYSTEM
Discovered by: Hugh Mann hughmann () hotmail com
Tested progs : Ipswitch WS_FTP Server 4.0.2.EVAL

A user who can upload files, and also has a max number of files limit or max total file size limit, can read any memory address the WS_FTP Server can read. With the right address, the user can cause a buffer overflow and execute arbitrary code as SYSTEM.

There's a vulnerability in the ALLO handler when it sends an error string to the client. Instead of pushing an ASCIIZ string, it pushes a 64-bit value equal to total size of all files in user's dir and any sub-dirs. This is a value we can easily control if we exploit the WS_FTP Server REST vulnerability. If we change this value to a string of size equal to ~256 bytes, we can overwrite the return address and execute arbitrary code as SYSTEM.

See the attached source code.

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Attachment: xp_ws_ftp_server2.zip

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