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Showing posts from 2016

All your Paypal OAuth tokens belong to me - localhost for the win

tl;dr  I was able to hijack the OAuth tokens of EVERYPaypal OAuth application with a really simple trick.
Introduction If you have been following this blog you might have got tired of how many times  I have stressed out the importance of the redirect_uri parameter in the OAuth flow.
This simple parameter might be source of many headaches for any maintainer of OAuth installations being it a client or a server.
Accepting the risk of repeating myself here is two simple suggestions that may help you stay away from troubles (you can always skip this part and going directly to the Paypal Vulnerability section):
If you are building an OAuth client,   Thou shall register a redirect_uri as much as specific as you can
i.e. if your OAuth client callback is https://yourouauthclient.com/oauth/oauthprovider/callback then

DO register https://yourouauthclient.com/oauth/oauthprovider/callbackNOT JUST https://yourouauthclient.com/ or https://yourouauthclient.com/oauth If you are still not convinced here…

The RFC 5114 saga

Back in January I posed a question "to the Internet": What the heck is RFC 5114?
It looks like a lot happened since then around it. I would like to use this post to recollect some of the stuff around RFC5114 .

Chapter 0: October 2007
RFC5114 draft was submitted to the IETF .

Chapter I: January 2016
In short RFC5114 is an IETF Informational RTC that "describes eight Diffie-Hellman groups that can be used in conjunction with IETF protocols to provide security for Internet communications." . One of the thing about this RTC that attracted the attention of many (and also mine) is that violates the Nothing up my sleeve principle. The other peculiar thing about this RTC (that caught my attention) was that the Ps specified for groups 22/23/24 were not safe primes but were indeed DSA primes adapted to Diffie Hellman. So far so good. Except that all the p-1 specified for those groups factored in a really nice way! So I decided to intensify a bit my research and found someth…

Native applications with OAuth 2

By Justin Richer and Antonio Sanso  This article was excerpted from the book OAuth 2 in Action.
The OAuth core specification specifies four different grant types: Authorization Code, Implicit, Resource Owner Password Credentials and Client Credentials. Each grant type is designed with different security and deployment aspects in mind and should be used accordingly.  For example, the Implicit grant flow is to be used by OAuth clients where the client code executes within the user agent environment. Such clients are generally JavaScript-only applications, which have, of course, limited capability of hiding the client_secret in client-side code running in the browser. At the other side of the spectrum there are classic server-side applications that can use the authorization code grant type and can safely store the client_secret somewhere in the server. What about native applications then?  Native applications are those that run directly on the end user’s device, be it a computer or mobil…

Holy redirect_uri Batman!

If you bought the book I have been writing with Justin Richer namely OAuth 2 in Actionyou might have noticed that we will never got tired to stress out how much important the redirect_uri is in the OAuth 2 universe. Failing to understand this (rather simple) concept might  lead to disasters. The redirect_uri is really central in the two most common OAuth flows (authorization code and implicit grant). I have blogged about redirect_uri related vulnerability severaltimes and both in OAuth client and OAuth server context.  Developing an OAuth client is notoriously easier to develop compare to the server counter part. Said that the OAuth client implementer should still take care and master some concepts.  If I would be limited to give a single warning for OAuth client implementer this would be 
If you are building an OAuth client,   Thou shall register a redirect_uri as much as specific as you can
or simply less formally "The registered redirect_uri must be as specific as it can be&quo…

Google Chrome Potential leak of sensitive information to malicious extensions (CVE-2016-1658)

Last Google Chrome release for Chrome 50.0.2661.75 contains the fix for a security low bug I found (CVE-2016-1658).
When first I found this bug I was under the impression it could be an UXSS. Quickly after I reported I started to realize that this wasn't as exploitable though.
The issue per se was extremely easy to reproduce:

Create an HTML file that looks like and save it (e.g. chrome.html)
<h1>Hi</h1> 
<script> alert(document.domain)</script>
Now supposing the file is saved under (in MacOS) /Users/xxx/Downloads/chrome.html open the file from hard disk in this way:

file://mail.google.com/Users/xxx/Downloads/chrome.html

Note: mail.google.com is arbitrary . This can be any domain (hence is universal) 
Observe the document.domain alerted is mail.google.com!

 Observe the cookies transported are the one associated with *.google.com domain :

Now this looked really weird to me and I reported as an UXSS. Pretty quickly though was cleat that the file: URL has a unique o…

OpenSSL Key Recovery Attack on DH small subgroups (CVE-2016-0701)

Usual Mandatory Disclaimer: IANAC (I am not a cryptographer) so I might likely end up writing a bunch of mistakes in this blog post...

tl;dr The OpenSSL 1.0.2 releases suffer from a Key Recovery Attack on DH small subgroups. This issue got assigned CVE-2016-0701 with a severity of High and OpenSSL 1.0.2 users should upgrade to 1.0.2f. If an application is using DH configured with parameters based on primes that are not "safe" or not Lim-Lee (as the one in RFC 5114) and either Static DH ciphersuites are used or DHE ciphersuites with the default OpenSSL configuration (in particular SSL_OP_SINGLE_DH_USE is not set) then is vulnerable to this attack.  It is believed that many popular applications (e.g. Apache mod_ssl) do set the  SSL_OP_SINGLE_DH_USE option and would therefore not be at risk (for DHE ciphersuites), they still might be for Static DH ciphersuites.
Introduction So if you are still here it means you wanna know more. And here is the thing. In my last blog post I was …

What the heck is RFC 5114?

Mandatory Disclaimer: IANAC (I am not a cryptographer) so I might likely end up writing a bunch of mistakes in this blog post...

I already talked about Diffie–Hellman (DH from now on) in TLS in my previous post: Small subgroup attack in Mozilla NSS.
As mentioned FWIW I strongly agree with Google Chrome decision to deprecate DHE .
The reason is mainly due to the Weak Diffie-Hellman attack and related paper . If you are interested in this topic there is a really nice presentation about it at 32C3 .
This shows a really nice potential attack that anyone with enough computational power (let's say NSA) can perform against DHE 1024 bits (details in the paper).
Said that for some reason I have been looking at DHE for a while now and one day I hit RFC 5114.

Now what the heck is this specification about :S ?

I found only few references about it. One funny one from here says (emphasis mine):



There is a semi-mysterious RFC 5114 – Additional Diffie-Hellman Groups document. It introduces new M…