Re: Growing Bad Practice with Login Forms

[Rogan Dawes <discard () dawes za net>]

Mark Curphey wrote:

> I am seeing more and more sites implementing a bad practice with login
> forms.
>
> To pick on a high profile site that should know better take ISACA as an
> example.
>
> http://www.isaca.org/
>
> In the top left hand corner you will see their secure login button and a
> graphical padlock embedded into the HTML. Of course if you look at the form
> tags, this does indeed submit the form over SSL and in the process the SSL
> handshake checks the certificate and my browser should verify that I am
> indeed sending my password to isaca.org. 
>
> But at that point its too late. The check for server authentication is done
> after I have sent by username and password. This IMHO is a bad practice that
> has started to creep into other sites including online banking. 

Not so much "too late", I think. If the check fails, the username and 
password will not be sent, unless you accept the certificate error.

Client -------------------- Server
TCP Syn   ->
          <- TCP SYN/ACK
TCP ACK   ->
Initiate SSL handshake ->
...
verify server cert OK
-> POST /xxxxxxx
-> username=x&password=y
<- 200 Ok

The above sequence would abort prior to the POST, with no compromise of 
the credentials, IFF the certificate is incorrect.

The issue really seems to be that you have no proof that the HTML page 
that is displaying the form is legit. In my experience, it is very 
unusual for people to verify the destination of a login form by checking 
the source to the page.

So the page displaying the form could be completely bogus, forged, 
delivered through a MITM, etc, with the form destination changed to 
whatever the attacker chooses. That seems to be the "reason" that this 
is bad practice.

In my opinion (and echoing yours, I'd say), either users should be 
invited to click a link taking them to a secure login page, or all pages 
that display login boxes should be served over HTTPS.

Obviously, if your site template includes a login box, such that all 
pages have one, this could mean running your entire site over SSL. In 
such a case, it would be better to have a link to a secure login page.

Rogan
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Rogan Dawes

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