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Is it possible to grab hidden code in ClientForm?

 
 
Muddy Coder
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      03-01-2009
Hi Folks,

Nowadays some websites let users to fill in some so-called
verification code, and the tricky thing is that the CODE is delivered
from server with an image. For example:

<img src="/jobsearch/captcha.jpg" name="CAPTCHA_IMAGE" border="1" /
>&nbsp;&nbsp;<a href="#" onClick="changeSource();">Refresh Image</a>


When click Refresh Image, the CODE on the image changes. I wonder:
does the server really send a new image over to browser, or just send
a hidden code over? Is it possible to parse out such hidden code?

The other example is:

<img src="/images/verify.png;jsessionid=ahZsBmwyLGuf" alt="Digital
Signature Code" />
<input name="jsessionid" type="hidden" value="ahZsBmwyLGuf" />

I did a few REFRESH on browser, and noticed the CODE changed. But,
when I viewed the HTML source code, the value "ahZsBmwyLGuf" remained
the same. What is the trick around here? That is why I am wondering
whether the server really keeps sending new images over, or just
sending new hidden codes over. If the trick is just keep sending
hidden codes over, there might be a chance of capturing the codes. Can
somebody help me out? Thanks a lot!


Muddy Coder





 
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Gabriel Genellina
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      03-01-2009
En Sun, 01 Mar 2009 12:23:20 -0200, Muddy Coder <(E-Mail Removed)>
escribió:

> Nowadays some websites let users to fill in some so-called
> verification code, and the tricky thing is that the CODE is delivered
> from server with an image. For example:
>
> <img src="/jobsearch/captcha.jpg" name="CAPTCHA_IMAGE" border="1" /
>> &nbsp;&nbsp;<a href="#" onClick="changeSource();">Refresh Image</a>

>
> When click Refresh Image, the CODE on the image changes. I wonder:
> does the server really send a new image over to browser, or just send
> a hidden code over? Is it possible to parse out such hidden code?


The server may asociate the expected value (CODE) to some session ID.
Delivering a new image means a new value associated. No other changes are
needed in the client side.

--
Gabriel Genellina

 
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rdmurray@bitdance.com
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      03-01-2009
Muddy Coder <(E-Mail Removed)> wrote:
> Nowadays some websites let users to fill in some so-called
> verification code, and the tricky thing is that the CODE is delivered
> from server with an image. For example:
>
> <img src="/jobsearch/captcha.jpg" name="CAPTCHA_IMAGE" border="1" /
> >&nbsp;&nbsp;<a href="#" onClick="changeSource();">Refresh Image</a>

>
> When click Refresh Image, the CODE on the image changes. I wonder:
> does the server really send a new image over to browser, or just send
> a hidden code over? Is it possible to parse out such hidden code?
>
> The other example is:
>
> <img src="/images/verify.png;jsessionid=ahZsBmwyLGuf" alt="Digital
> Signature Code" />
> <input name="jsessionid" type="hidden" value="ahZsBmwyLGuf" />
>
> I did a few REFRESH on browser, and noticed the CODE changed. But,
> when I viewed the HTML source code, the value "ahZsBmwyLGuf" remained
> the same. What is the trick around here? That is why I am wondering
> whether the server really keeps sending new images over, or just
> sending new hidden codes over. If the trick is just keep sending
> hidden codes over, there might be a chance of capturing the codes. Can
> somebody help me out? Thanks a lot!


If there were some way for a program to extract the code from what
the server sent, then the whole point of using the Captcha (preventing
spam robots from posting) would be defeated.

--RDM

 
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