> On Jan 21, 2016, at 2:50 PM, John Bradley <ve7...@ve7jtb.com> wrote: > > In that case you probably would put a hash of the state in the code to manage > size. The alg would be up to the AS, as long as it used the same hash both > places it would work. Yes, true. > > Sending the state to the token endpoint is like having nonce and c_hash in > the id_token, it binds the issued code to the browser instance. I think I understand what you are saying. Someone won’t be able to frankenstein up a state and a token from two different responses from an AS, and have a client successfully fetch an access token based on the amalgamation. > This protects against codes that leak via redirect uri pattern matching. > failures etc. It prevents an attacker from being able to replay a code from > a different browser. Yes, if a party intercepts the redirect_url, or the AS fails to enforce one time use (which even for a compliant implementation could just mean the attacker was faster than the state propagated within the AS)
Makes sense. Thanks John. -DW > If the client implements the other mitigations on the authorization endpoint, > then it wouldn't be leaking the code via the token endpoint. > > The two mitigations are for different attacks, however some of the attacks > combined both vulnerabilities. > > Sending the iss and client_id is enough to stop the confused client attacks, > but sending state on its own would not have stopped all of them. > > We discussed having them in separate drafts, and may still do that. However > for discussion having them in one document is I think better in the short run. > > John B. > >> On Jan 21, 2016, at 4:48 PM, David Waite <da...@alkaline-solutions.com >> <mailto:da...@alkaline-solutions.com>> wrote: >> >> Question: >> >> I understand how “iss" helps mitigate this attack (client knows response was >> from the appropriate issuer and not an attack where the request was answered >> by another issuer). >> >> However, how does passing “state” on the authorization_code grant token >> request help once you have the above in place? Is this against some >> alternate flow of this attack I don’t see, or is it meant to mitigate some >> entirely separate attack? >> >> If one is attempting to work statelessly (e.g. your “state” parameter is >> actual state and not just a randomly generated value), a client would have >> always needed some way to differentiate which issuer the authorization_code >> grant token request would be sent to. >> >> However, if an AS was treating “code” as a token (for instance, encoding: >> client, user, consent time and approved scopes), the AS now has to include >> the client’s state as well. This would effectively double (likely more with >> encoding) the state sent in the authorization response back to the client >> redirect URL, adding more pressure against maximum URL sizes. >> >> -DW
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