Re: [OAUTH-WG] Report an authentication issue

Nat Sakimura <> Sat, 16 June 2012 00:16 UTC

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Date: Sat, 16 Jun 2012 09:16:42 +0900
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From: Nat Sakimura <>
To: Francisco Corella <>
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Cc: matake nov <>, Yuchen Zhou <>, oauth <>, "Shuo Chen (MSR)" <>
Subject: Re: [OAUTH-WG] Report an authentication issue
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As to how the fix was done, Nov can provide more detail, but ...

1. Properly verify the signature/HMAC of the "signed_request". This will
essentially audience restricts the token.
2. There is an undocumented API for Facebook which returns to whom the
token was issued. This also audience restricts the token.

The service that fixed took these measures. Note that none of the above is
defined in OAuth.
The same facility was called "id_token" and "check ID endpoint" for OpenID

The scale of the impact is large, too large to disclose the actual names in
the public list, though, eventually, we would publish them in a paper.


On Sat, Jun 16, 2012 at 5:34 AM, Francisco Corella <>wrote:

> Hi Nat and Rui,
> Rui, you say that the vulnerability that you found was due to a
> "common misunderstanding among developers", but the attack you
> describe can be carried out against any app that uses the OAuth
> "implicit grant flow", which Facebook calls "client-side
> authentication".  No misunderstanding seems necessary.  What
> misunderstanding are you referring to?  I followed the link in your
> message to the Sophos post, and from there the link to the article in
> The Register.  The article in The Register says that Facebook had
> "fixed the vulnerability promptly".  How did they fix it?  The
> instructions that Facebook provides for implementing "Client-side
> authentication without the JS SDK" at
> still allows the attack.
> Nat, I agree that the blog post by John Bradley that you link to
> refers to the same vulnerability reported by Rui.  You say that some
> apps have issued a patch to fix it.  Could you explain what the fix
> was?
> Francisco
>   ------------------------------
> *From:* Nat Sakimura <>
> *To:* rui wang <>
> *Cc:* matake nov <>; Yuchen Zhou <>;
> oauth <>; Shuo Chen (MSR) <>
> *Sent:* Thursday, June 14, 2012 1:50 PM
> *Subject:* Re: [OAUTH-WG] Report an authentication issue
> This is a fairly well known (hopefully by now) issue. We, at the OpenID
> Foundation, call it "access_token phishing" attack these days. See:
> Nov Matake has actually built the code on iPhone to verify the problem,
> and has notified bunch of parties back in February including Facebook and
> Apple. We have the code that actually runs on a phone, and we have
> successfully logged in to bunch of apps, including very well known ones.
> They were all informed of the issue. Some immediately issued a patch to fix
> it while others have not.
> The problem is that even if these apps gets fixed, the problem does not go
> away. As long as the attacker has the vulnerable version of the app, he
> still can impersonate the victim. To stop it, the server side has to
> completely disable the older version, which means the service has to cut
> off many users pausing business problems.
> Nat
> On Fri, Jun 15, 2012 at 2:18 AM, rui wang <> wrote:
> Dear Facebook Security Team and OAuth Standard group,
> We are a research team in Microsoft Research. In January, 2011, we
> reported a vulnerability in Facebook Connect which allowed everyone to sign
> into Facebook-secured relying parties without password. It was promptly
> fixed after reporting. (
> )
> Recently, we found a common misunderstanding among developers of
> mobile/metro apps when using OAuth (including Facebook’s OAuth) for
> authentication. The vulnerability resulted from this misunderstanding also
> allows an attacker to log into a victim user's account without password.
> Let's take Soluto's metro app as an example to describe the problem. The
> app supports Facebook Login. As an attacker, we can write a regular
> Facebook app. Once the victim user allows our app to access her Facebook
> data, we receive an access_token from the traffic. Then, on our own machine
> (i.e., the "attacker" machine), we run the metro app of Soluto, and use a
> HTTP proxy to insert the victim's access_token into the traffic of Facebook
> login. Through this way, we are able to log into the victim's Soluto
> account from our machine. Other than Soluto, we also have confirmed the
> same issue on another Windows 8 metro-app Givit.
> The Facebook SDK for Android apps (
> seems to
> have the possibility to mislead developers too. At least, the issue that we
> found is not clearly mentioned. In the SDK, we ran the sample code called
> "Hackbook" using Android Emulator (imagine it is an attacker device). Note
> that we have already received the access token of the victim user from our
> regular Facebook app. We then inject the token to the traffic of Hackbook.
> Through this way, Hackbook app on our own machine recognizes us as the
> victim. Note that this is not a convincing security exploit yet, because
> this sample code does not include the server-side code. However, given that
> we have seen real server-side code having this problem, such as Soluto,
> Givit and others, we do believe that the sample code can mislead
> mobile/metro developers. We also suspect that this may be a general issue
> of many OAuth implementations on mobile platforms, so we send this message
> to OAuth Standard group as well.
> We have contacted the vendors of the two vulnerable metro-apps, Soluto and
> Gavit.
> Please kindly give us an ack when you receive this message. If you want to
> know more details, please let us know.
> Best Regards,
> Yuchen Zhou, Rui Wang, and Shuo Chen
> _______________________________________________
> OAuth mailing list
> --
> Nat Sakimura (=nat)
> Chairman, OpenID Foundation
> @_nat_en
> _______________________________________________
> OAuth mailing list

Nat Sakimura (=nat)
Chairman, OpenID Foundation