Agreed, I see you point about the big providers using exactly the
unrestricted flow for which the trust model (by definition) is out of
scope of the spec. This may be the reason for the implemented behavior
indeed and a security consideration is a good idea for other
deployments; there's not much more that can be done.
But Google also provides explicit registration for API clients (which is
where my mind was):
https://developers.google.com/accounts/docs/OAuth2 (step 1)
and they would not need to deviate from the spec for that, nor would the
spec need to change
Hans.
On 9/4/14, 9:50 AM, Antonio Sanso wrote:
Hi Hans,
I really fail to see how this can be addressed at registration time for cases
where registration is unrestricted (namely all the big Providers)
regards
antonio
On Sep 4, 2014, at 9:47 AM, Hans Zandbelt <hzandb...@pingidentity.com> wrote:
Classifying like this must also mean that consent should not be stored until
the client is considered (admin) trusted, and admin policy would interfere with
user policy.
IMHO the security consideration would apply only to dynamically registered
clients where registration is unrestricted; any other form would involve some
form of admin/user approval at registration time, overcoming the concern at
authorization time: there's no auto-redirect flow possible for unknown clients.
Hans.
On 9/4/14, 9:04 AM, Richer, Justin P. wrote:
I think this advice isn't a bad idea, though it's of course up to the AS
what an "untrusted" client really is. In practice, this is something
that was registered by a non-sysadmin type person, either a dynamically
registered client or something available through self-service
registration of some type. It's also reasonable that a client, even
dynamically registered, would be considered "trusted" if enough time has
passed and enough users have used it without things blowing up.
-- Justin
On Sep 4, 2014, at 1:26 AM, Antonio Sanso <asa...@adobe.com
<mailto:asa...@adobe.com>> wrote:
hi again *,
after thinking a bit further IMHO an alternative for the untrusted
clients can also be to always present the consent screen (at least
once) before any redirect.
Namely all providers I have seen show the consent screen if all the
request parameters are correct and if the user accepts the redirect
happens.
If one of the parameter (with the exclusion of the client id and
redirect uri that are handled differently as for spec) is wrong though
the redirect happens without the consent screen being shown..
WDYT?
regards
antonio
On Sep 3, 2014, at 7:54 PM, Antonio Sanso <asa...@adobe.com
<mailto:asa...@adobe.com>> wrote:
Well,
I do not know if this is only dynamic registration...
let’s talk about real use cases, namely e.g. Google , Facebook ,
etc.. is that dynamic client registration? I do not know… :)
Said that what the other guys think? :)
Would this deserve some “spec adjustment” ? I mean there is a reason
if Google is by choice “violating” the spec right? (I assume to avoid
open redirect…)
But other implementers do follow the spec hence they have this open
redirector… and this is not nice IMHO...
On Sep 3, 2014, at 7:40 PM, Hans Zandbelt <hzandb...@pingidentity.com
<mailto:hzandb...@pingidentity.com>> wrote:
On 9/3/14, 7:14 PM, Antonio Sanso wrote:
On Sep 3, 2014, at 7:10 PM, Hans Zandbelt
<hzandb...@pingidentity.com <mailto:hzandb...@pingidentity.com>> wrote:
Is your concern clients that were registered using dynamic client
registration?
yes
I think your issue is then with the trust model of dynamic client
registration; that is left out of scope of the dynreg spec (and the
concept is not even part of the core spec), but unless you want
everything to be open (which typically would not be the case), then
it would involve approval somewhere in the process before the client
is registered. Without dynamic client registration that approval is
admin based or resource owner based, depending on use case.
Otherwise the positive case is returning a response to a valid URL
that belongs to a client that was registered explicitly by the
resource owner
well AFAIK the resource owner doesn’t register clients…
roles can collapse in use cases especially when using dynamic client
registration
and the negative case is returning an error to that same URL.
the difference is the consent screen… in the positive case you need
to approve an app.. for the error case no approval is needed,,,
I fail to see the open redirect.
why?
because the client and thus the fixed URL are explicitly approved at
some point
Hans.
Hans.
On 9/3/14, 6:56 PM, Antonio Sanso wrote:
On Sep 3, 2014, at 6:51 PM, Hans Zandbelt
<hzandb...@pingidentity.com <mailto:hzandb...@pingidentity.com>
<mailto:hzandb...@pingidentity.com>> wrote:
Let me try and approach this from a different angle: why would you
call it an open redirect when an invalid scope is provided and
call it
correct protocol behavior (hopefully) when a valid scope is
provided?
as specified below in the positive case (namely when the correct
scope
is provided) the resource owner MUST approve the app via the consent
screen (at least once).
Hans.
On 9/3/14, 6:46 PM, Antonio Sanso wrote:
hi John,
On Sep 3, 2014, at 6:14 PM, John Bradley <ve7...@ve7jtb.com
<mailto:ve7...@ve7jtb.com>
<mailto:ve7...@ve7jtb.com>
<mailto:ve7...@ve7jtb.com>> wrote:
In the example the redirect_uri is vlid for the attacker.
The issue is that the AS may be allowing client registrations with
arbitrary redirect_uri.
In the spec it is unspecified how a AS validates that a client
controls the redirect_uri it is registering.
I think that if anything it may be the registration step that
needs
the security consideration.
(this is the first time :p) but I do disagree with you. It would be
pretty unpractical to block this at registration time….
IMHO the best approach is the one taken from Google, namely
returning
400 with the cause of the error..
*400.* That’s an error.
*Error: invalid_scope*
Some requested scopes were invalid. {invalid=[l]}
said that I hope you all agree this is an issue in the spec so
far….
regards
antonio
John B.
On Sep 3, 2014, at 12:10 PM, Bill Burke <bbu...@redhat.com
<mailto:bbu...@redhat.com>
<mailto:bbu...@redhat.com>
<mailto:bbu...@redhat.com>> wrote:
I don't understand. The redirect uri has to be valid in
order for a
redirect to happen. The spec explicitly states this.
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 thevictim.com
<http://thevictim.com/>
<http://victim.com/><http://victim.com <http://victim.com/>
<http://victim.com/>>
<http://victim.com <http://victim.com/> <http://victim.com/>>
provider.
I register redirect uriattacker.com <http://uriattacker.com/>
<http://attacker.com/><http://attacker.com
<http://attacker.com/> <http://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
<http://attacker.com/>
<http://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
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