Outlook.com for Android fails to validate server certificates

Outlook.com for Android fails to validate server certificates

Yorick Koster, April 2014

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

Tested versions

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

See also

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

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]

Introduction

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.

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