SEC Consult Vulnerability Lab Security Advisory < 20111219-1 >
=======================================================================
              title: Multiple vulnerabilities in WhatsApp 
            product: WhatsApp (tested on Android client) 
      fixed version: -
           impact: Medium  
           homepage: http://www.whatsapp.com/
              found: 2011-09-09
                 by: G. Wagner         
                     SEC Consult Vulnerability Lab 
                     https://www.sec-consult.sg
=======================================================================

Vendor description:
-------------------
WhatsApp Messenger is a cross-platform mobile messaging app which
allows to exchange messages without having to pay for SMS. In addition
to basic messaging iPhone, Android, Nokia and BlackBerry WhatsApp
Messenger users can send each other images, video and audio media
messages.


Issue 1: Updating arbitrary users' status
-----------------------------------------
The WhatsApp does most of its communication through XMPP, in some cases
though the client sends HTTPS requests to interact with the server.
This is the case when the client fetches a users' status, as well as
for updating it. By providing any WhatsApp registered telephone number
and the text for the status update, it is possible to change a user's
status. This action does not require any prior authentication or
authorization (This issue was last tested 2011-12-07).

No POC will be published as no fix is available.


Issue 2: Registration bypass
----------------------------
The second issue concerns the registration process. One method to
verify a phone number is through a text message that is sent to the
phone. So if the entered phone number is not yet registered with a
specific udid a HTTP GET request is sent to /v1/code.php.

This action triggers a SMS to be sent to the phone number that is
supposed to be registered. The SMS contains a 3 digit code for example
"WhatsApp code 101". If the client receives the SMS it would send the
code to the server through /v1/register.php to verify it.

This function can be easily bruteforced and therefore an arbitrary phone
number can be registered. The vendor has implemented bruteforce
protection by locking a number after 10 tries. This step makes a
successful attack on a specific number unlikely but an attacker
bruteforcing X00 numbers can still guess X number(s) on average.


Issue 3: Usage of plain text protocols 
--------------------------------------
As published in the past several times already the XMPP traffic from
WhatsApp is not encrypted. So if an attacker is able to perform a
Man-in-the-middle attack it would be possible to read for example
received or sent messages and even modify them. The response from the
vendor did not indicate that there is a concrete plan to resolve this
issue in the future.


Vendor contact timeline:
------------------------
2011-09-14: Initially contacted vendor 
2011-09-14: Contact established to security team and sent advisory.
            Asked for feedback and patch timeline.
2011-09-23: No response from vendor. Asked for feedback and patch
            timeline.
2011-09-23: Vendor response asking for clarification
            regarding issue 2.
2011-10-14: Response sent regarding issue 2. 
2011-10-26: No response from vendor. Asked for feedback and patch
            timeline.
2011-11-02: Feedback from vendor regarding issue 2. 
2011-11-02: Asked for patch timeline of the other issues and coordinated
            publication.
2011-12-07: No response from vendor. Informed vendor of last chance to
            provide a patch timeline within 7 work days.
2011-12-14: No response from vendor. 
2011-12-19: Public release without POC


Recommendations:
----------------
WhatsApp users are advised to confirm messages with important content
on a different communication channel.


Advisory URL:
-------------
https://www.sec-consult.sg/advisories.html


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EOF G. Wagner / @2011