On Tue, 03 Jan 2012 18:34:01 -0500, Igor Faynberg wrote:
Well, this exchange made me read all I could find on reverse proxies.
Now I understand--and agree with--the last statement of AYJ: '"the
server" is a proxy. '
But my understanding is that the proxy (which DNS pointed me to when
I tried to get to my bank) belongs in the domain "mybank," and this
proxy had been issued a valid certificate--which I had ascertained in
the process of authentication. So, the end result is that the proxy
is
part of the bank. If we expect it to be harmful to the bank--so we
could the "server" itself as well as any bank's employee. It would
be
the bank replaying things to itself, right?
I'm not sure we quite match ideas on this. The problem is between the
client and proxy. Not between the proxy and the server. Here is a
transaction sequence for that bank:
client 1 to proxy:
GET /?oauth_token=FOO HTTP/1.1
Host: bank.example.com
proxy to server:
GET /?oauth_token=FOO HTTP/1.1
Host: bank.example.com
(server verifies the token "FOO" is valid for client 1 through the
proxy)
bank server to proxy:
HTTP/1.1 200 OK
stuff
proxy to client 1:
HTTP/1.1 200 OK
stuff
.. some time passes. The token "FOO" expires, gets replaced by token
"FOO-2".
client 1 to proxy:
GET /?oauth_token=FOO-2 HTTP/1.1
Host: bank.example.com
proxy to server:
GET /?oauth_token=FOO-2 HTTP/1.1
Host: bank.example.com
(server verifies the token "FOO-2" is valid for client 1 through the
proxy)
bank server to proxy:
HTTP/1.1 200 OK
other-stuff
proxy to client 1:
HTTP/1.1 200 OK
other-stuff
Attacker processes some URL records they somehow swiped from the client
transactions...
attacker to proxy:
GET /?oauth_token=FOO HTTP/1.1
Host: bank.example.com
proxy to attacker:
HTTP/1.1 200 OK
stuff
... Oops.
attacker to proxy:
GET /?oauth_token=FOO-2 HTTP/1.1
Host: bank.example.com
proxy to attacker:
HTTP/1.1 200 OK
other-stuff
... Oops.
I assume for clarity that the server and client 1 have both correctly
implemented Bearer and are performing proper validation and expiry on
the query-string tokens.
The mitigation is for the server which implements Bearer to be sending
Cache-Control with one of the values: no-store, private,
proxy-revalidate and/or must-revalidate.
AYJ
Then it is the bank's problem, not OAuth's as far as I am
concerned...
Igor
On 1/2/2012 7:36 PM, Amos Jeffries wrote:
On 1/2/2012 7:07 AM, Amos Jeffries wrote:
On 2/01/2012 11:00 p.m., Torsten Lodderstedt wrote:
...
general note: I do not understand why caching proxies should
impose a problem in case TLS is used (end2end). Could you please
explain?
Because TLS is hop-by-hop (in HTTP hops, end-to-end only in TCP
hops). Proxies which decrypt TLS and provide responses out of cache
are already deployed in many places. Mostly in the form of
reverse-proxies, but corporate decryption proxies are also on the
increase.
AYJ
On 3/01/2012 11:17 a.m., Igor Faynberg wrote:
I am at a loss here; granted, it is a gray area... Does it mean
that RFC 2817 has not been implemented properly?
From RFC 2817:
"
5. Upgrade across Proxies
As a hop-by-hop header, Upgrade is negotiated between each pair
of
HTTP counterparties. If a User Agent sends a request with an
Upgrade
header to a proxy, it is requesting a change to the protocol
between
itself and the proxy, not an end-to-end change.
"
The more common case is CONNECT method from RFC 2068, from a user
agent to a reverse-proxy. Same behaviour.
To make it simple: At the client, I establish a session key with
the server, and then use it for confidentiality. How is this key
known to any proxy?
"the server" is a proxy.
AYJ
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