Can server hack client ?

Kookies is one example of where the server 'writes into' the client,
right ?

Redirection is another example where the server 'controls the client',
instead of just being a passive read-only device ?

Java [script]: the grossest example of the server messing with you can
of course be disabled. Where is a list of 'actions' whereby a server
can 'control'/write-to eg. my plain lynx client which doesn't want to
be written to ?

Thanks for any info.

== Chris Glur.

(E-Mail Removed) said:
>Kookies is one example of where the server 'writes into' the client,
> right ?

Yes.

>Redirection is another example where the server 'controls the client',
>instead of just being a passive read-only device ?

In a way, yes. Redirect, however, is one of the reply formats to be
expected from a server.

>Java [script]: the grossest example of the server messing with you can
>of course be disabled. Where is a list of 'actions' whereby a server
>can 'control'/write-to eg. my plain lynx client which doesn't want to
>be written to ?

If it just was that simple - and if the chain was just that short.
As a naive example, consider the server sending a deliberately
malformed response - f.ex. claiming to send a response of 2000 bytes,
and then sending more than that. A naive client implementation
could f.ex. reserve a receive buffer of 2000 bytes when seeing
the Content-length - and still stream in all of the content sent
by the server, thus overwriting the buffer, and perhaps resulting
in the buffer data flowing over to some executable area.

Further, if I recall correctly, even Lynx can be configured to start
external helper programs for certain data types (such as xpdf,
acroread or something for data declared to be PDF documents). Now,
consider that the servers sends some malformed content that is
then processed by such external program. How does the external
program handle it?

I hope this helps, at least in showing that the issue is not
quite straightforward.
--
Wolf a.k.a. Juha Laiho Espoo, Finland
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Juha Laiho <(E-Mail Removed)> wrote:
> (E-Mail Removed) said:
> >Kookies is one example of where the server 'writes into' the client,
> > right ?
> Yes.

I would have phrased the answer a little differently. The server
says, "Here, set this cookie." But the client is free to ignore that.
Really, it's the client that writes the cookie, at the suggestion of the
server.


> >Redirection is another example where the server 'controls the client',
> >instead of just being a passive read-only device ?
> In a way, yes. Redirect, however, is one of the reply formats to be
> expected from a server.

I would not have said that the server ever "controls the client". I
guess it's true in the very general sense that if the server sends a
redirect, the client will follow the redirect, but that's what it's
designed to do, because of the protocol... And the server is _never_ a
"passive read-only device". The server is always disallowing some
requests, redirecting some, remapping others, etc. I suppose one
could write a webserver that ignored permissions, used the root of the
filesystem as the document root, didn't know anything about redirects,
etc., but
a) this would be dumb
b) it doesn't bear much relation to how real webservers actually work.

I think the OP needs to learn a little more about how TCP and HTTP
work in order to ask useful questions. Not intended as a slam at anyone
- just a suggestion.

--
Oh to have a lodge in some vast wilderness. Where rumors of oppression
and deceit, of unsuccessful and successful wars may never reach me
anymore.
-- William Cowper