Ahh… After re-reading, you’re examining using
artifact model for the AuthnRequest. I guess that is possible with the new
artifact->message binding in 2.0, though I haven’t seen anybody
actually implement it that way. This would reduce the processing at the IdP
of the AuthnRequest message to only doing so for trusted SPs but it also
requires that the SP maintain an artifact resolution service – in most deployments
they work to ease the requirements on the SP since there typically are more SPs
than IdPs, so I wouldn’t see them easily adopting the overhead to deal
with an artifact resolution service (it’s not simple).
Conor
From: Cahill, Conor P
Sent: Monday, June 30, 2008 8:46 AM
To: ;
Subject: RE: Artifact binding -- Most effective binding against DOS
attacks
The IdP must expose a means by which an SP can obtain the
artifact. This is the standard AuthnReqest entry point (I don’t
know the metadata element off the top of my head) where the SP redirects the
browser to in order to initiate SSO from the IdP. That’s
still needed in the artifact model (which typically involves SP sending
AuthnRequest to IdP through users browser, IdP responding to SP with Artifact
through user’s browser, and finally SP dereferencing artifact on back
channel directly with IdP).
So, even if you use the Artifact profile, you still need the
browser based AuthnRequest exchange in order to get the artifact to the
SP. Since the IdP has to support AuthnRequest, the attacker
could still use this channel for a direct DOS attack.
Conor
From: giorgi moniava
[mailto:]
Sent: Monday, June 30, 2008 7:18 AM
To: ; Cahill, Conor P
Subject: RE: Artifact binding -- Most effective binding against DOS
attacks
Hi Conor.
With point (b) you make a good point about implicit DOS attacks in SAML
2.0.
However, I don't get your statement: "The IDP still has a AuthnRequest entry point for SSO requests
and must process the request as necessary and thus that interface could still
be used for enabling a DOS attack by flooding the IdP with bazillions of
AuthnRequests long before you ever get to the stage of artifact
dereference. "
To my knowledge, an IdP first receives an artifact (using an HTTP
redirect), and then, it
contacts the corresponding SP (who is the owner of the artifact), and aks
to resolve the
received artifact. If at this stage, authentication and access control are
combined, then
IdP will make sure that she won't receive any resolved messages from
illegimitate SPs'. Also, once an SP will be recorded as malicious, IdP will
refure to resolve artifacts from that SP in the future.
Further, just wondering, why could not SAML 2.0 design artifacts such
that, at the time of their receival, both parties could be able to make sure
that the received artifact was generated by a legitimate party. This way, DOS
attacks would be efficiently and effectively avoided -- i.e. without the need
to contact partner entities for resolving invalid artifacts.
Giorgi.
--- On Mon, 6/30/08, Cahill, Conor P <>
wrote:
From: Cahill, Conor P
<>
Subject: RE: Artifact binding -- Most effective binding against DOS attacks
To: ,
Date: Monday, June 30, 2008, 4:05 AM
In
reality, I think that the artifact profile will have limited, if any, impact
on DOS attacks. The IDP still has a AuthnRequest entry point for
SSO requests and must process the request as necessary and thus that
interface could still be used for enabling a DOS attack by flooding the IdP
with bazillions of AuthnRequests long before you ever get to the stage of
artifact dereference.
At first
glance one might think that the artifact profile will save the IdP from
having to generate the signed Assertion since attackers are not trusted
SPs. However, a) in a DOS attack the IdP usually won¢t be
generating an assertion anyway since the logins will typically fail, and b)
if the attacker does have good credentials (so the IdP would end up
creating a good authn session and have to generate assertions at some point),
they could still get the assertions to be generated by doing an indirect DOS
attack using a multitude of good SPs and driving the IdP attack through those
SPs (the attacker essentially initiates Authn sessions at the SPs causing the
SPs to flood the IdP with authnRequests & artifact resolutions).
So, from a
DOS point of view, I think it doesn¢t make a difference.
Of course,
there are many other good reasons to use the artifact profile.
Conor
From: giorgi moniava
[mailto:]
Sent: Monday, June 30, 2008 3:48 AM
To: ; Cahill, Conor P
Subject: Artifact binding -- Most effective binding against DOS
attacks
Hi all.
Just wanted to ask your opinion about following statement. I think that
artifact based binding has the highest chances to be effectively secured
against DOS attacks. Since, when an IdP received an artifact, which comes
from an malicious SP, and tries to contat her in order to retrieve the
corresponding
message using SOAP binding, she will use SSL/TLS with bilateral
authentication,
clearly, if she looks up the identitied of the available parties then,
requests from
malicious SPs will be blocked (i.e. IdP wont receive SAML 2.0 messages from
them, just artifacts). With POST and GET bindings, IdP is forced to process
a SAML 2.0 message before she can take any action for protecting against
DOS.
Does what I wrote make sense?
Thanks!.
Giorgi.
