[keycloak-dev] Issue with concurrent SSO login to same client in more browser tabs

[Marek Posolda]

On 26/11/2018 08:54, Stian Thorgersen wrote:
> The ideal may be to create a code token. If it's less than 2000 
> characters just send it as is. If it's more than we put it in the 
> actionTokens cache and just send a reference to it in the code param.
I see. So it will be something like "hybrid" between both approaches. 
Was also a bit thinking about it, but didn't in the end. ATM it is 
always adding the item to actionTokens cache. Maybe it's possible to 
optimize it and add the "hybrid" possibility, but not sure about it at 
this stage? Maybe after new year?
> Not sure if the reference should just be a uuid, or if it should be 
> something more to make sure it can't be guessed. The last point is 
> also relevant to reference tokens once/if we add support for that.

ATM it is <code-uuid>.<user-session-id>.<client-uuid>

The userSessionId and clientUUID are needed, so if code was already used 
(and is removed from actionTokens cache), it is still possible to lookup 
userSession and remove clientSession from it as OIDC specs suggests (in 
case that attempt of duplicate code use was detected).

Not sure how big probability is to guess UUID for the very short-lived 
code. It seems to me like kind of impossible thing. And if it's really 
guessed, then when valid user will try to exchange the code, which 
attacker already exchanged, the "code" will be expired (client removed 
from userSession as pointed above).

Marek

>
> On Mon, 19 Nov 2018 at 11:49, Marek Posolda <mposolda at redhat.com 
> <mailto:mposolda at redhat.com>> wrote:
>
>     Hi,
>
>     I've sent PR https://github.com/keycloak/keycloak/pull/5736 to fix
>     the
>     issue in subject (corresponding JIRAs are KEYCLOAK-7774
>     KEYCLOAK-8438).
>     The cause is that once the user is authenticated in the browser
>     and has
>     userSession, there is just 1 clientSession per the
>     userSession+client.
>     So in case of concurrent SSO login in more browser tabs, there can
>     be an
>     issue that each tab is writing it's state to the same clientSession,
>     which causes conflicts (especially attributes like nonce, scope or
>     redirectUri can be possibly different for each tab and shouldn't be
>     shared).
>
>     The possibility can be to revert back when we had more clientSessions
>     per userSession+client. I think this is step back and has lots of
>     other
>     issues (memory consumption, more cluster and cross-dc writes, worse
>     performance in general...). For the future, it will be rather
>     ideal to
>     remove clientSession entirely or reduce their size even more, as they
>     will be needed for logout, but hopefully for nothing more.
>
>     So the other possibility is to move most of the state to the "code"
>     parameter and to the refreshToken. Each browser tab has it's own
>     "code"
>     and it's own refreshToken. Problem with the "code" is, that it's
>     used as
>     query parameter in the URL and hence has limits for it's size. It
>     seems
>     ideal is still to stick with 2000 characters per URL. And when
>     redirectUri itself will be part of the code, it can be problematic
>     as we
>     don't know how the redirectUri provided by users will be big....
>     Fortunately refreshToken doesn't have this issue as it needs to be
>     always sent in the POST request.
>
>     So to solve the issue for "code", I've added an entry to the
>     infinispan
>     cache "actionTokens", which encapsulates needed state and it's
>     supposed
>     to be valid just for the very short time (between the
>     AuthenticationResponse to the application and the time when
>     application
>     sends the code-to-token request) and it's lifespan corresponds to
>     realm
>     code lifespan (1 minute by default). In the code-to-token request,
>     there
>     is a call to "cache.remove" to remove the code. Infinispan caches
>     (local, distributed and hotrod caches) fortunately guarantee that
>     "remove(123)" is always successful just in 1 thread (Successful means
>     that it returns previous state). So we still have guarantee for the
>     single-use code.
>
>     Marek
>
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