[NT] Serv-U FTP Server Long Filename Stack Overflow Vulnerability

From: SecuriTeam (support_at_securiteam.com)
Date: 01/26/04

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Date: 26 Jan 2004 16:09:46 +0200

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      Serv-U FTP Server Long Filename Stack Overflow Vulnerability
    ------------------------------------------------------------------------

    SUMMARY

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

    An internal memory buffer may be overrun while handling "site chmod"
    command with a filename containg excessive data. This condition could lead
    to a server compromise and ultimately to execute instructions with the
    server's priviledges.

    DETAILS

    Vulnerable Systems:
     * Serv-U FTP server versions prior to 4.2 including 4.1.0.11

    Immune Systems:
     * Serv-U FTP server version 5.0

    While exectuing chmod on a nonexistent file, Serv-U will call sprintf to
    construct the response string. The code resembles the following:

    sprintf(dst, "%s: No such file or directory.", filename);

    The length of the dst buffer is only 256 bytes. If a long filename was
    received, Serv-U will crash. A writable directory is needed in order to
    exploit this vulnerablity. By overwriting the SEH (Structured Exception
    Handler), we can create a proof-of-concept exploit on Win2K/XP.

    Patch Availability:
    The bug has been fixed in Serv-U version 5.0.

    ADDITIONAL INFORMATION

    The information has been provided by <mailto:icbm@0x557.net> All members
    of SST

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