bugtraq - Outlook.com for Android fails to validate server certificates

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Message-ID: <53F10802.4040900@securify.nl>
Date: Sun, 17 Aug 2014 21:52:34 +0200
From: "Securify B.V." <lists@...urify.nl>
To: bugtraq@...urityfocus.com
Subject: Outlook.com for Android fails to validate server certificates

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Outlook.com for Android fails to validate server certificates
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Yorick Koster, April 2014

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Abstract
------------------------------------------------------------------------
Outlook.com for Android's WebView contains an insecure SSL error handler
that ignores any certificate validation errors. Due to this, it is
possible to perform a man in the middle attack against this app. The
vulnerable component is uses to log into outlook.com. A successful
attack allows sniffing of login credentials (user name & password).

Demonstration:
http://vimeo.com/101999863

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Tested versions
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This issue was found in Outlook.com for Android version 7.8.2.12.49.2176
and version 7.8.2.12.49.6434.

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See also
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- CVE-2014-5239 [2]
- JVNDB-2014-000086 [3] Outlook.com for Android contains an issue where
it fails to verify SSL server certificates

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Fix
------------------------------------------------------------------------
A new version (7.8.2.12.49.7090) of Outlook.com for Android was released
in which the affected SSL error handler is no longer present. The latest
version of Outlook.com for Android can be obtained from Google Play [4]

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Introduction
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When logging into outlook.com, Outlook.com for Android will load
login.live.com in a WebView. This WebView has implemented a custom SSL
error handler [5], which basically ignores any certificate validation
errors.

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Insecure error handler
------------------------------------------------------------------------
The affected SSL error handler can be found in the
AuthorizationWebViewClient inner class of
com.microsoft.live.AuthorizationRequest$OAuthDialog. The relevant code
is listed below.

public void onReceivedSslError(WebView paramWebView, SslErrorHandler
paramSslErrorHandler, SslError paramSslError)
{
AuthorizationRequest.OAuthDialog.this.setLiveSdkProvProgressStatus(false);
         paramSslErrorHandler.proceed();
}

As can be seen in this listing, the method gets an SslErrorHandler
instance named paramSslErrorHandler. The handler calls proceed() [6],
which will ignore any certificate error and the connection will be
created. Due to this, any invalid certificate will also be accepted,
even the attacker's certificate rendering the app vulnerable to man in
the middle attacks. Since this issue exists within a login component, it
is possible to steal Microsoft account login credentials, which is
usually an Outlook.com email address and password.
------------------------------------------------------------------------
References
------------------------------------------------------------------------
[1] 
http://www.securify.nl/advisory/SFY20140403/outlook_com_for_android_fails_to_validate_server_certificates.html
[2] http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2014-5239
[3] http://jvndb.jvn.jp/en/contents/2014/JVNDB-2014-000086.html
[4] https://play.google.com/store/apps/details?id=com.outlook.Z7
[5] 
http://developer.android.com/reference/android/webkit/WebViewClient.html#onReceivedSslError%28android.webkit.WebView,%20android.webkit.SslErrorHandler,%20android.net.http.SslError%29
[6] 
http://developer.android.com/reference/android/webkit/SslErrorHandler.html#proceed%28%29