The Hack Lair

Case study: Reading memory content

By using Logcat and Wireshark we were able to get a lot of interesting information but we can go deeper into the system. The Android Developer Studio include multiple tools we can use. It allow us to check memory allocations, generate memory dumps, view thread executions, get performance statistics, etc. In this case, we want to investigate the app memory content.

First, we need to install Android Studio, and get it running, which isn’t an easy process. If you are running Ubuntu, you can use this custom repository.

sudo apt-add-repository ppa:paolorotolo/android-studio
sudo apt-get update
sudo apt-get install android-studio default-jdk lib32z1 lib32ncurses5 lib32bz2-1.0 lib32stdc++6

This will not install the latest version but we don’t need it.

Pro tip: You can install an operating system without affecting your current configuration with software like Virtual Box.

Once installed, lets start Android Studio and create a blank project. Then we can connect our device to our computer via a USB cable and start monitoring via “Tools >> Android >> Android Device Monitor”.

If you are having problems connecting your device, unlock it, fire up the console and type in adb shell. You will need to authorize your computer. A pop-up will ask you to validate the computer finger print.

Once Android Device Monitor is running you’ll see a list of device process on the left tab. From there, we can pick a process and activate profiling by clicking Update Heap and Update Threads. Information will appear on the right tab. We can also use the logcat output at the bottom. Use adb shell ps | grep | cut -c10-15 to get the process id and filter out other app logs.

This part get a bit technical. You will see Java execution threads and will have to dig out what is what. For example I stumbled upon “Okio Watchdog” and Googled it. The app use the Okio external library to manage it’s input/output .

That’s quite interesting but what we want to get is the memory content. For that we will need to create a heap dump, a memory snapshot. On the top of the process list there’s a button called Dump HPROF file. That’s what we need.

In order to analyze that file we need to download Java Visual VM. Anroid heap dumps aren’t in the format JVM need but we can convert it with hprof-conv It’s a binary from Android Studio. You’ll need to find it on your computer. Now fire up visualvm and open the converted hprof.

Now we can browse Java objects instances, which in Java is pretty much everything. You can also use the OQL console, a query tool. Check the Visual VM Object Query Language documentation to get a basic understanding.

Ok so what do we have from this dump?

With the OQL console we can search strings for with the help of a regex.

select s.toString() from java.lang.String s where /regex/(s.toString())

There’s way to much info in there…

Analyzing Aptoide with those tools wasn’t that benificial. We didn’t learn much. But if we need to look at memory content at a later point we’ll have no problem finding what we need.

Other posts from the Android forensics and security analysis series: