Wednesday, 18 September 2013

WeChat IM Application vulnerable to Attackers in Android - 9/17/2013 12:57:00 PM

WeChat is a feature-rich and sophisticated mobile application, which allows users to communicate via text messages, voice calls, to share photos and videos, and much more. The app is available for several mobile platforms, but we focused on the Android version only: according to Google Play, WeChat for Android alone has more than 50 million downloads. Most of the issues discussed in this post should affect Android versions of WeChat up to 4.5.1. On August 5th, 2013, Tencent released version 5.0, which introduced some major changes; we still have to analyze this version in detail.

From a security perspective, the remote logging feature is surely the most interesting one. By exploiting this functionality, an attacker can develop a malicious application which exposes the aforementioned ContentProvider and, through specially-crafted debug settings, makes WeChat to send logs to an external, attacker-controlled, server. Such a malicious application would not require any special Android permission.

It is worth considering that logged messages disclose sensitive information about the users, including the user ID, password hash and other details. As an example, here is an excerpt from a remote log session: 

09-09 14:32:51 594 V/MicroMsg.MMBuiltInIP <-- br="" dump="" end="" mmbuiltinip=""> 09-09 14:32:51 626 D/MicroMsg.AccInfo update session info: session=, uin=-1893467821
09-09 14:32:51 635 I/MicroMsg.AutoAuth sending remote request,
09-09 14:32:51 666 I/MicroMsg.AutoAuth.SceneInfoQueue inQueue: netid=0
09-09 14:32:51 691 V/MicroMsg.SDK.SyncTask sync task done, return=0, cost=56(wait=0, run=56)
09-09 14:32:51 783 V/MicroMsg.NetStatWatchDog dkreport status:9999002 nowCount:1 ret:1
09-09 14:32:51 810 D/MicroMsg.AutoAuth account info updated:AccInfo:
|-uin =-1893467821
|-user =ukcd_ao03gex3y2731v
|-session =
|-pass =5f4dcc3b5aa765d61d8327deb882cf99
|-pass2 =5f4dcc3b5aa765d61d8327deb882cf99
`-cookie =(null)
09-09 14:32:51 885 D/MicroMsg.NetStatWatchDog item.toByteArray() :433
09-09 14:32:52 101 D/MicroMsg.GYNet encoding, type=380, key=, time=284
09-09 14:32:52 108 I/MicroMsg.GYNet sendImp reqData.len:866
09-09 14:32:52 114 D/MicroMsg.NetStatusUtil activeNetInfo extra=internet, type=0

As can be seen from these logs, the application forwards to the remote server the user name (ukcd_ao03gex3y2731v), another user identifier (uin, with value -1893467821), and even the user's password hash (5f4dcc3b5aa765d61d8327deb882cf99). It should be noted the hash value is a plain MD5 of the user's password, sent to the server for the authentication. Obviously some parameters in the above logs have been edited to prevent readers from hacking our account but, yes,5f4dcc3b5aa765d61d8327deb882cf99 is the MD5 for string "password" and this was really our account's password :-) 

The next section details the communication protocol used by WeChat to interact with the remote log server. 

Remote logging protocol

Remote logging can be enabled by configuring the following debug keys: 
  • = 0
  • = :
  • = :
The first key defines the log level ("0" simply means to log everything), while others are used to set the log server address for the two main WeChat application modules (mm and push). 

You can Read more about the Attack Scenario in Original Post here

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