JEB in Action

Let’s have a quick look at a variant of Android.Uracto, an app that steals (and potentially spams) contacts from Android devices. There is nothing particularly interesting about this piece of malware, but it’s the occasion to demonstrate some of JEB less-known and forthcoming abilities.

Upon startup, the app displays the following spinner, that translates to “Reading the articles…”:

The onCreate() method for the main activity displays the above spinner, and also starts a new Thread, that will create and run a Progress object. Here it is:

The run() method will call postMailList(). This method gets the ContentResolver for the app, and enumerates all entries having the “vnd.android.cursor.item/name” MIME type. According to the documentation, these entries represent “contacts’ proper names”.

A buffer representing the data1, data2, and data3 fields (respectively, Display Name, Given Name, and Family Name) is dynamically created.

[JEB specific]

Notice the optimizations that allowed the creation of that compact construct:

• for-loop optimization
• string concatenation
• aggressive variable substitution

Some of these optimizations are already present in 1.0.x, others will be included in the 1.1 versions.

[/JEB specific]

The final data (“contact1, contact2, …”) is dumped on the external memory storage, encoded and POST’ed to hxxp://jap2012.com/data/main.php.

Find the decompiled activity here: solution.newsandroid.MainviewActivity

Sample MD5: ba73e96caa95999321c1cdd766bdf58b

Let’s inaugurate this blog by looking at a fairly simple piece of Android malware, an SMS interceptor app whose prime targets are South Korean users.

The app impersonates a Starbucks coupon (스타벅스 쿠폰) app.

Let’s check the decompiled Java code.

When the user starts the app, it displays a fake error message, indicating that the server is out-of-service, and terminates. In the meantime, it has registered and started the malicious service com.catchspam.catchservice.

Notice that a preference variable “runYN” is set to “execute” (실행.) More on it later.

The malicious service does two things:
– First, it registers the cellphone number by POST’ing it to hxxp://it7980.com/Android_SMS/installing.php. (If the number is Korean and starts with the prefix +82, it receives “special treatment”.)
– Then, it registers a BroadcastReceiver meant to process incoming text messages.

The BroadcastReceiver com.catchspam.catchsms2 processes SMS_RECEIVED intents. The last PDU is processed and (supposedly) contains the text message.

In the following screenshot, notice that the author implemented a minimal C&C-like behavior:
– If the text reads “execute”, the runYN preference variable will also be set to “execute”.
– If the text matches the “magic passphrase”, that variable will be set to “pause”. (It roughly translates to: “Back and forth the same versus luck ♥ Lee ♥ ♥ Please call 1588-1588”.)
Later, runYN is checked and the interception procedure will bail if it is not set to “execute”. This allows the author to enable/disable the interception, either globally or for specific phone numbers.

The intent broadcast is cancelled to prevent other apps (and eventually, the user) from processing the SMS. Finally, the message is POST’ed to the author’s server. The data format is “mobile=<number>&revsms=<textmessage>”.

SMS stealers can be simple annoyance or steal personal data. In this case, it might be used to capture 2-factor authentication codes sent by online banking websites.

Download the sample here.