[NT] Serv-U STOU Command DoS

From: SecuriTeam (support_at_securiteam.com)
Date: 09/15/04

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Date: 15 Sep 2004 12:05:57 +0200

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      Serv-U STOU Command DoS
    ------------------------------------------------------------------------

    SUMMARY

    " <http://www.serv-u.com/> Serv-U is a powerful, easy-to-use,
    award-winning FTP server created by Rob Beckers".

    Using special identifiers that exists under the Windows operating system
    in conjunction with the STOU FTP command will cause Serv-U to crash
    immediately.

    DETAILS

    Vulnerable Systems:
     * Serv-U FTP server versions 5.2 and prior

    While processing the STOU command, Serv-U does not properly limit what is
    passed as input and in fact will attempt to write the uploaded file as the
    identifier passed. Since the following listed identifiers are special
    system file objects and Serv-U's code is not careful, trying to write to
    any of them will force Windows to shut down the offending server. The
    vulnerability is readily available for exploitation by any logged on user,
    even anonymous. In order to exploit it, one of the following commands
    should be sent to the server:
    STOU COM1
    STOU LPT1
    STOU PRN
    STOU AUX

    Note however that the NUL identifier does NOT trigger a crash of the
    server. All others will cause the server to crash immediately.

    ADDITIONAL INFORMATION

    The information has been provided by <mailto:patrickthomassen@gmail.com>
    Patrick.

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