Re: Web Forms filtered with SQL constraints

[RSnake <rsnake () shocking com>]

        Nothing you do at the client side can be hidden.  I can write a
        client that downloads the source, or watch it via a proxy, or
        look at the cache, etc....  don't even bother trying.  You
        should consider anything client side as protection from
        inadvertant mistakes by users only, and you should always have a
        fall back filter in place to catch the errors before they do any
        damage.

On Wed, 6 Oct 2004, Ian wrote:

| Date: Wed, 06 Oct 2004 09:52:03 +0100
| From: Ian <webappsec2 () fishnet co uk>
| Reply-To: webappsec () securityfocus com
| To: "[ISO-8859-1] B?noni MARTIN" <Benoni.MARTIN () libertis ga>,
|     webappsec () securityfocus com
| Subject: Re: Web Forms filtered with SQL constraints
| 
| On 5 Oct 2004 at 13:25, B?noni MARTIN wrote:  
| 
| > Hi list ! 
| > 
| > I was wondering how to solve the 2 following problems: I have ASP (not
| > ASP.NET) formulaires people have to fill in. To avoid SQ injection attacks
| > and other tricks, I have set up some Jscript filtering on each field (i.e.
| > for instance a name can just be alphabet's characters and no figures :) ),
| > and I am planning to do the same on my Database (setting up constraints). 
| > 
| > 
| > But I have 2 questions:     - How can I hide my Jscript filtering from the
| > user ? When I want to see the source, everything is diaplayed, quite
| > normal :( ... Maybe it's not so good to tell people what I have done to
| > filter them :) I saw some sites where it is impossible to see the source,
| > impossible to "hoover the site", impossible even to print ... But I have
| > not been able to find on the net how to do this :( 
| > 
| >     - How can I deal with possible SQL errors within an ASP page ? I mean, if
| > a field has been filled in, bypass my Jscript filtering (no matter how),
| > and gets to the database but is then "stopped" by an SQL onstraint, how do
| > I raise this error on an ASP page without diplaying an explicit error
| > (giving the user the name of my database for instance) ? 
| > 
| > Cheers for any clue, I am lost on this topic :( 
| 
| Hi,
| 
| Using classic ASP with vbscript you would add this to the top of the page:
| 
| <% on error resume next %>
| 
| Then after every SQL query:
| 
| <% 
| if err then
|       Response.write "There was a database error"
|       ' Log to error to file
| end if
| %>
| 
| I think the equivalent in JScript is the Try, Catch, Finally:
| 
| http://msdn.microsoft.com/library/default.asp?url=/library/en-
| us/script56/html/js56jslrfjscripterrorstoc.asp
| 
| Hope this helps
| 
| Ian
| -- 
| 
| 
| 
| 
| 

-R

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