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Phishing Google Wallet and Paypal by abusing WhatsApp
From: Curesec Research Team <crt () curesec com>
Date: Wed, 24 Jul 2013 16:52:01 +0200

Hi List,

please find the vulnerability description within this post.

Cheers,
 Curesec Research Team

Reference:
https://cureblog.de/2013/07/phishing-google-wallet-and-paypal-by-abusing-whatsapp/


Phishing Google Wallet and Paypal by abusing WhatsApp

-=Introduction=-

WhatsApp is one of the most common used tools aka ‘Apps’ on
Smarphone-Devices with access to wireless networks or a so called
Data-’Flatrate’. By using the internet link to communicate, people do
not have to pay any extra fees for sending a text-message somewhere,
even if the receiver is in another country.

WhatsApp is available for almost every architecture on the market. The
program exists for Nokia, Blackberry, Android and iOS. It is available
here: https://www.whatsapp.com. This post will focus on the version for
android.

The app is free for one-year in Android devices. After that time the
user has to buy a yearly license. The application provides 3 methods of
payment:

    google wallet
    paypal
    payment link.

They can be selected via Menu->Settings->Account->Payment Info.

-=Bug=-

Google-wallet and Paypal payments work in the same way. When selecting
it, WhatsApp opens an in-app browser and contacts its main server
www.whatsapp.com with the request:

/payments/google.php?phone=XXXXXXXXXXXX&cksum=<request
checksum>&sku=1&lg=en&lc=US

or

/payments/paypal.php?phone=XXXXXXXXXXXX&cksum=<request
checksum>&sku=1&lg=en&lc=US

Responding to this request the browser gets redirected to the proper
checkout service.
The payment link option seems to be currently not working, i.e., nothing
happens.

-=Attacks=-

Even tough the communication with the payment systems is HTTPS secured,
the initial contact with the main server www.whatsapp.com is NOT, as we
can see in Wireshark logs:

GET
/payments/google.php?phone=xxxxxxxxxxxxx&cksum=<checksum>&sku=1&lg=en&lc=US
HTTP/1.1
Host: www.whatsapp.com
Accept-Encoding: gzip
Accept-Language: en-US
User-Agent: Mozilla/5.0 (Linux; U; Android 2.3.7)
Cookie: __utmmobile=0xxxxxxxxxxxxxxxxxxxx
Accept:application/xml,application/xhtml+xml,text/html;
q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
Accept-Charset: utf-8, iso-8859-1, utf-16, *;q=0.7

After Whatsapp sent this unencrypted request, it will receive the
following answer.

HTTP/1.1 200 OK
X-Powered-By: PHP/5.4.7
Content-type: text/html
Transfer-Encoding: chunked
Date: Mon, 10 May 2013 05:34:36 GMT
Server: lighttpd/1.4.31
5e4

<html>
<head>
<meta name="HandheldFriendly" content="true"/>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>WhatsApp Messenger payment</title>
</head>
<body onLoad="document.getElementById('google').submit()">
<p>Please wait...</p>
<form id="google" method="POST" action="https://checkout.google.com
api/checkout/v2/checkoutForm/Merchant/xxxxxxxxxxxxxx"
accept-charset="utf-8">
<input type="hidden" name="shopping-cart.items.item-1.item-name"
value="One year of WhatsApp service for phone XXXXXXXXXXXXXXX"/>
<input type="hidden" name="shopping-cart.items.item-1.item-description"
value="WhatsApp Messenger"/>
<input type="hidden" name="shopping-cart.items.item-1.merchant-item-id"
value="1"/>
<input type="hidden"
name="shopping-cart.items.item-1.merchant-private-item-data"
value="XXXXXXXXXXXXXXX"/>
<input type="hidden" name="shopping-cart.items.item-1.unit-price"
value="0.99"/>
<input type="hidden"
name="shopping-cart.items.item-1.unit-price.currency" value="USD"/>
<input type="hidden" name="shopping-cart.items.item-1.quantity" value="1"/>
<input type="hidden"
name="shopping-cart.items.item-1.digital-content.display-disposition"
value="OPTIMISTIC"/>
<input type="hidden"
name="shopping-cart.items.item-1.digital-content.email-delivery"
value="true"/>
<input type="hidden"
name="checkout-flow-support.merchant-checkout-flow-support.continue-shopping-url"
value="http://www.whatsapp.com/payments/success.php"/>
<input type="hidden" name="_charset_" />
</form>
</body>
</html>
0

This means an attacker could intercept the first request via a suitable
man-in-the-middle attack and successfully redirect the user to any
Webpage when the user is trying to buy Whatsapp credit. To gain
useraccounts the attacker could setup a fake Google-Wallet or Paypal
Systems page to harvest user accounts. It might even be possible to
gather directly money through this, for instance let the user pay the
0,99 cents via Google Wallet or Paypal to the account of the attacker.

Besides an attacker could forward some other content like a webpage with
a new apk necessary for using google-wallet or paypal, like the
(in)-famous Zitmo Trojan did at visiting a Bankingsite and spending
users some extra “Security”-Features.

-=Practical abuse of the bug=-

As buying the credit only happens one time per year the attack itself is
quite uncommon to be practical for a huge misuse as the attacker needs
to be in control of the wireless or gsm network to intercept and
redirect the traffic.

-=Affected Versions=-

2.9.6447 to 2.10.751 (latest as of 2013 July 2)


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