Re: [hybi] Handshake was: The WebSocket protocol issues.

[Adam Barth <[e-mail]>]

On Thu, Sep 30, 2010 at 6:50 PM, Scott Ferguson <[e-mail]> wrote:
> To repeat the key pieces:
>  a) c-nonce must not be available to or predictable by the hijacker
>  b) "WebSocket" is not possessed by a non-websocket server

You're making a bunch of assumptions about how non-websocket servers
behave.  In particular, consider a protocol like DNS.  It's entirely
possible that a DNS-like protocol could relay the c-nonce to the
attacker and give the attacker an opportunity to response with the
appropriate hash, which the server would then relay to the client.
Attacks of this general class (even against DNS) are known for HTTP.

The security of this protocol relies on more assumptions than you've
listed in your message.  Reasoning about security here is very subtle,
especially when reasoning about the behavior of non-WebSocket servers.
 We need to be prepared for them to do a wide variety of things.

As a side note, using an exotic HTTP method is not a good idea.  The
first few bytes of the clients initial message are absolutely
critical.  Picking an exotic HTTP method is just rolling the dice
w.r.t. what protocols an attacker can exploit.  For example, some
attacks from HTTP to DNS rely critically on the fact that the first
byte of an HTTP POST message is an uppercase P.  The kinds of things
you can do with an uppercase W as the first byte are largely
unstudied.

Adam