Doesn't step 7 require the evil user to know the client's secret?
Am 10.09.2010 17:06, schrieb Eran Hammer-Lahav:
1. Evil user starts the OAuth flow on the client using the web-server flow.
2. Client redirects the evil user to the authorization server, including state
information about the evil user account on the client.
3. Evil user takes the authorization endpoint URI and changes the redirection
to its own site.
4. Evil user tricks victim user to click on the link and authorize access
(phishing or other social engineering attack).
5. Victim user thinking this is a valid authorization request, authorizes
access.
6. Authorization server sends victim user back to the client, but since the
redirection URI was changed, back to the evil user site.
7. Evil user grabs the code and exchanges it for an access token.
By checking that the callback URI used to deliver the code is the same as the
one used to initiate the flow, the authorization server can verify that the
user who initiated the flow is the same one to authorize access and finish the
flow.
EHL
-----Original Message-----
From: oauth-boun...@ietf.org [mailto:oauth-boun...@ietf.org] On Behalf
Of Freeman, Tim
Sent: Wednesday, September 08, 2010 8:05 PM
To: oauth@ietf.org
Subject: [OAUTH-WG] Why give the redirect URI when trading an access
code for an access token?
Hi. I'm new here. I searched the archives a bit and didn't immediately find an
answer to my question below. My apologies if there was some previous
discussion of this that I missed.
Looking at the draft spec at http://tools.ietf.org/html/draft-ietf-oauth-v2-10,
I see in section 4.1.1 "Authorization code" on page 22 that it is required to
give the redirect_uri of the original request when exchanging an
authorization code for an access token, and the authorization server must
verify that the redirection URI is correct as well as the authorization code.
Based on section 4.2 "Access Token Response" on page 25, it seems that the
redirect_uri is not used when constructing the response from the
authorization server.
So far as I can tell, the redirect_uri is useless in this request. It does not
contain any secrets. The authorization code is verified and is meant to be an
arbitrary unguessable identifier, so little is gained by verifying the
redirect_uri also. It is not used to construct the reply. Why is it required?
Tim Freeman
Email: tim.free...@hp.com
Desk in Palo Alto: (650) 857-2581
Home: (408) 774-1298
Cell: (408) 348-7536
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