On Sep 3, 2014, at 6:10 PM, Bill Burke <[email protected]<mailto:[email protected]>> wrote:
I don't understand. The redirect uri has to be valid in order for a redirect to happen. The spec explicitly states this. the redirect uri is indeed valid. The wrong parameter is the scope. So if the attacker is the person that registers the app and register as redirect uri attacker.com<http://attacker.com> he can redirect anybody to attacker.com<http://attacker.com> levering the provider website uri… On 9/3/2014 11:43 AM, Antonio Sanso wrote: hi *, IMHO providers that strictly follow rfc6749 are vulnerable to open redirect. Let me explain, reading [0] If the request fails due to a missing, invalid, or mismatching redirection URI, or if the client identifier is missing or invalid, the authorization server SHOULD inform the resource owner of the error and MUST NOT automatically redirect the user-agent to the invalid redirection URI. If the resource owner denies the access request or if the request fails for reasons other than a missing or invalid redirection URI, the authorization server informs the client by adding the following parameters to the query component of the redirection URI using the "application/x-www-form-urlencoded" format, perAppendix B <https://tools.ietf.org/html/rfc6749#appendix-B>: Now let’s assume this. I am registering a new client to the victim.com<http://victim.com/> <http://victim.com<http://victim.com/>> provider. I register redirect uri attacker.com<http://attacker.com/> <http://attacker.com<http://attacker.com/>>. According to [0] if I pass e.g. the wrong scope I am redirected back to attacker.com<http://attacker.com/> <http://attacker.com<http://attacker.com/>>. Namely I prepare a url that is in this form: http://victim.com/authorize?response_type=code&client_id=bc88FitX1298KPj2WS259BBMa9_KCfL3&scope=WRONG_SCOPE&redirect_uri=http://attacker.com and this is works as an open redirector. Of course in the positive case if all the parameters are fine this doesn’t apply since the resource owner MUST approve the app via the consent screen (at least once). A solution would be to return error 400 rather than redirect to the redirect URI (as some provider e.g. Google do) WDYT? regards antonio [0] https://tools.ietf.org/html/rfc6749#section-4.1.2.1 _______________________________________________ OAuth mailing list [email protected]<mailto:[email protected]> https://www.ietf.org/mailman/listinfo/oauth -- Bill Burke JBoss, a division of Red Hat http://bill.burkecentral.com<http://bill.burkecentral.com/> _______________________________________________ OAuth mailing list [email protected]<mailto:[email protected]> https://www.ietf.org/mailman/listinfo/oauth
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