Decrypting APT33’s Dropshot Malware with Radare2 and Cutter – Part 2

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 Prologue

Previously, in the first part of this article, we used Cutter, a GUI for radare2, to statically analyze APT33’s Dropshot malware. We also used radare2’s Python scripting capabilities in order to decrypt encrypted strings in Dropshot. If you didn’t read the first part yet, I suggest you do it now.

Today’s article will be shorter, now that we are familiar with cutter and r2pipe, we can quickly analyze another interesting component of Dropshot — an encrypted resource that includes Dropshot’s actual payload. So without further ado, let’s start.

Downloading and installing Cutter

Cutter is available for all platforms (Linux, OS X, Windows). You can download the latest release here. If you are using Linux, the fastest way to use Cutter is to use the AppImage file.

If you want to use the newest version available, with new features and bug fixes, you should build Cutter from source by yourself. It isn’t a complicated task and it is the version I use.

First, you must clone the repository:

Building on Linux:


Building on Windows:

If any of those do not work, check the more detailed instruction page here

Dropshot \ StoneDrill

As in the last part, we’ll analyze Dropshot, which is also known by the name StoneDrill. It is a wiper malware associated with the APT33 group which targeted mostly organizations in Saudi Arabia. Dropshot is a sophisticated malware sample, that employed advanced anti-emulation techniques and has a lot of interesting functionalities. The malware is most likely related to the infamous Shamoon malware. Dropshot was analyzed thoroughly by Kaspersky and later on by FireEye. In this article, we’ll focus on decrypting the encrypted resource of Dropshot which contains the actual payload of the malware.

The Dropshot sample can be downloaded from here (password: infected). I suggest you star () the repository to get updates on more radare2 tutorials 🙂

Please, be careful when using this sample. It is a real malware, and more than that, a wiper! Use with caution!

Since we’ll analyze Dropshot statically, you can use a Linux machine, as I did.

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Decrypting APT33’s Dropshot Malware with Radare2 and Cutter – Part 1

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Prologue

As a reverse engineer and malware researcher, the tools I use are super important for me. I have invested hours and hours in creating the best malware analysis environment for myself and chose the best tools for me and my needs. For the last two years, radare2 is my go-to tool for a lot of reverse-engineering tasks such as automating RE related work, scripting, CTFing, exploitation and more. That said, I almost never used radare2 for malware analysis, or more accurately, for analysis of malware for Windows. The main reason was that radare2 command-line interface felt too clumsy, complicated and an over-kill. IDA Pro was simply better for these tasks, a quick inspection of functions, data structures, renaming, commenting, et cetera. It felt more intuitive for me and that what I was searching for while doing malware analysis. And then came Cutter.

 

Cutter

Along the years, the radare2 community had tried to develop many different graphic-interfaces for radare2. None of them came even close to Cutter. Cutter is a QT C++ based GUI for radare2. In my opinion, it is the GUI that radare2 deserves. To quote from Cutter’s Github page:

Cutter is not aimed at existing radare2 users. It instead focuses on those whose are not yet radare2 users because of the learning curve, because they don’t like CLI applications or because of the difficulty…

Cutter is a young project, only one-year-old, and it is the official GUI of radare2 (the first and only GUI to be announced “official”). Cutter is a cross-platform GUI that aims to export radare2’s plenty of functionality into a user-friendly and modern GUI. In this post, I’ll show you some of Cutter’s features and how I work with it. To be honest, Cutter is intuitive so you probably won’t need me to show you around, but just in case.

Downloading and installing Cutter

Cutter is available for all platforms (Linux, OS X, Windows). You can download the latest release here. If you are using Linux, the fastest way to use Cutter is to use the AppImage file.

If you want to use the newest version available, with new features and bug fixes, you should build Cutter from source by yourself. It isn’t a complicated task and it is the version I use.

First, you must clone the repository:

Building on Linux:


Building on Windows:

If any of those do not work, check the more detailed instruction page here.

Dropshot \ StoneDrill

Dropshot, also known as StoneDrill, is a wiper malware associated with the APT33 group which targeted mostly organizations in Saudi Arabia. Dropshot is a sophisticated malware sample, that employed advanced anti-emulation techniques and has a lot of interesting functionalities. The malware is most likely related to the infamous Shamoon malware. Dropshot was analyzed thoroughly by Kaspersky and later on by FireEye. In this article, we’ll focus on analyzing how Dropshot decrypted the strings inside it in order to evade analysis. In part 2 of this article, which will be published soon, we’ll focus on decrypting the encrypted resource of Dropshot which contains the actual payload of the malware.

The Dropshot sample can be downloaded from here (password: infected). I suggest you star () the repository to get updates on more radare2 tutorials 🙂

Please, be careful when using this sample. It is a real malware, and more than that, a wiper! Use with caution!

Since we’ll analyze Dropshot statically, you can use a Linux machine, as I did.

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Reversing a Self-Modifying Binary with radare2

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Prologue

It took me three months to finish writing this article. I had so many tasks on my to-do list that sadly this one was pushed down to the bottom of the list. Last weekend I made a promise to myself that until Sunday I’m going to finish writing it, I successfully kept my word and here it is, another radare2 tutorial.

Today we’ll solve a very nice challenge, “packedup”, written by ad3l for r2con 2017 competition. It is not the first writeup that I publish from r2con competition, you can check out “Reverse engineering a Gameboy ROM with radare2” as well, make sure not to miss the cool swags I got from winning the competition.

This article is aimed to those of you who are familiar with radare2. If you are not, I suggest you to start from part 1 of my series “A Journey Into Radare2”.

So, without further ado, let’s dig into the binary.

 

Getting radare2

Installation

Radare2’s development is pretty quick – the project evolves every day, therefore it’s recommended to use the current git version over the stable one. Sometimes the stable version is less stable than the current git version!

If you don’t want to install the git version or you want the binaries for another machine (Windows, OS X, iOS, etc.) check out the download page at the radare2 website.

Updating

As I said before, it is highly recommended to always use the newest version of r2 from the git repository. All you need to do to update your r2 version from the git is to execute:

And you’ll have the latest version from git. I usually update my version of radare2 in the morning with a scheduled task, so I can wake up to the latest version available. If you’re using radare2 often, I recommend you do the same.

packedup

You can download packedup from here. I suggest you to star () the repository to get updates about more radare2 tutorials 🙂

First thing to do, obviously, is to execute the binary and get a basic feeling of what we are going to face.

packedup is executed, it requests us to give it a flag. It then probably does some calculations at the backend to see if the inputted flag is the right one. I entered “MEGABEETS” which is likely not the correct flag and finished with the fail message — “Try again!”.

Reversing time!

Now for our favorite part, let’s open the binary with radare2 and try to figure out how packedup is checking the submitted flag:

$ r2 ./packedup
— Here be dragons.
[0x004004d0]>
aaa
[x] Analyze all flags starting with sym. and entry0 (aa)
[x] Analyze len bytes of instructions for references (aar)
[x] Analyze function calls (aac)
[*] Use -AA or aaaa to perform additional experimental analysis.
[x] Constructing a function name for fcn.* and sym.func.* functions (aan)

Analysis

I usually begin with executing aa (analyze all) or with aas (to analyze functions, symbols and more). The name is misleading because there is a lot more to analyze (check aa?) but it’s enough to start with for most of the binaries I examined. This time we’ll start straight with aaa to make things simpler and due to the binary’s small size. You can also run radare2 with the -A flag to analyze the binary straight at startup using aaa (e.g r2 -A ./packedup).

Note: as I mentioned in the previous posts, starting with aaa is not always the recommended approach since analysis is very complicated process. I wrote more about it in this answer — read it to better understand why.

Getting Information

So now that we opened our binary with radare2, we have been located automatically at the program’s entrypoint. But before we start working on the code itself It’s a good approach to get to know our binary characteristics. radare2 can show us the information we need using the i command (I removed some information for the sake of readability):

The i command used for getting info about the opened file. It’s a wrapper around rabin2 which is an information extractor tool in the radare2 framework. radare2 offers us tons amount of information about the binary. Check out i? to list the information’s subcommands.

packedup is a 64-bit stripped ELF binary. Cool. Let’s move on.

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Reverse engineering a Gameboy ROM with radare2

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 Prologue

A month ago in Barcelona I was attending to r2con for the first time. This is the official congress of the radare2 community where everyone can learn more about radare2 framework and dive deep into different aspects of reverse engineering, malware analysis, fuzzing, exploiting and more. It also the place where all of us, the contributors and developers of radare2, can meet, discuss and argue about every other line of code in the framework.

This was the second congress of radare2, after the success of the first congress in last year which was also a celebration for radare’s 10 years old birthday. This year the conference was bigger, fancier and probably organized much better. r2con was four days long, starting at September 6 and lasted until September 9. The first two days were dedicated to training and took place at Universitat de Barcelona. The other two days were talks days and took place at the MediaPro.

Crackmes Competition

During r2con this year there was a Crackmes competition where all the attendees were given with the same 5 challenges and had to publish a writeups to all the challenges they had solved. The scoring was based on the quality of the writeups along with the quantity of solved challenges.

I won the competition and got myself some cool swag!

  • Flag of radare2
  • POC | GTFO book
  • Orange PI with 3D printed case of r2con logo
  • Radare2 stickers
  • A beer 🍺

 

I thought of sharing some of my writeups with you, so you can taste a bit from what we had in the competition and so that others, coming from google, twitter and such, could learn how to use radare2 for solving different challenges. This article is aimed to those of you who are familiar with radare2. If you are not, I suggest you to start from part 1 of my series “A Journy Into Radare2”.

Getting radare2

Installation

Radare2’s development is pretty quick – the project evolves every day, therefore it’s recommended to use the current git version over the stable one. Sometimes the stable version is less stable than the current git version!

If you don’t want to install the git version or you want the binaries for another machine (Windows, OS X, iOS, etc) check out the download page at the radare2 website.

Updating

As I said before, it is highly recommended to always use the newest version of r2 from the git repository. All you need to do to update your r2 version from the git is to execute:

And you’ll have the latest version from git. I usually update my version of radare2 in the morning, while watching cat videos.

 

Playing with Gameboy ROM

This post will describe how I solved simple.gb, a Gameboy ROM challenge written by @condret. It was actually my first time reversing a Gameboy ROM — and it was awesome!

First thing I did was to open the binary in radare2 and check for its architecture and format:

$ r2 simple.gb
— For a full list of commands see strings /dev/urandom
[0x00000100]> i~format
format   ningb
[0x00000100]> i~machine
machine  Gameboy

The i command gives us information about the binary. Check i? for more commands.

Tilde (~) is r2’s internal grep.

Surprise, surprise, it is a Gameboy ROM — dah. After reading a bit about its instruction set we should go to the mission. 

The obvious thing to do is open the ROM in an Gameboy emulator. I downloaded the good old emulator I used back in the days when I played Pokemon: VisualBoy Advance.

Let’s open the ROM in our emulator and see what we have:


Woops, wrong file. Bad habits… Let’s try again:

Cool! It’s a simple game where, by using the arrow keys, you increase/decrease 5 digits. We ‘simply’ need to find the correct password.

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A journey into Radare 2 – Part 2: Exploitation

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Prologue

Welcome back to the second part of our journey into the guts of radare2! In this part we’ll cover more of the features of radare2, this time with the focus on binary exploitation.

A lot of you waited for the second part, so here it is! Hope to publish the next part faster, much faster. If you didn’t read the first part of the series I highly recommend you to do so. It describes the basics of radare2 and explains many of the commands that I’ll use here.

In this part of the series we’ll focus on exploiting a simple binary. radare2 has many features which will help us in exploitation, such as mitigation detection, ROP gadget searching, random patterns generation, register telescoping and more. You can find a Reference Sheet at the end of this post. Today I’ll show you some of these great features and together we’ll use radare2 to bypass nx protected binary on an ASLR enabled system. I assume that you are already familiar with the following prerequisites:

It’s really important to be familiar with these topics because I won’t get deep into them, or even won’t briefly explain some of them.

Updating radare2

First of all, let’s update radare2 to its newest git version:

We have a long journey ahead so while we’re waiting for the update to finish, let’s get some motivation boost — cute cats video!

 

Getting familiar with our binary

You can download the binary from here, and the source from here.
If you want to compile the source by yourself, use the following command:

Our binary this time is quite similar to the one from the previous post with a few slight changes to the main() function:

  • Compiled without -z execstac to enable NX bit
  • Receives user input with scanf and not from program’s arguments
  • Uses mostly puts to print to screen
  • Little changes to the program’s output

This was the previous main():

 

And now main looks like this:

 

The functionality of the binary is pretty simple and we went through it in the previous post — It asks for user input, performs rot13 on the input and compares it with the result of rot13 on the string “Megabeets”. Id est, the input should be ‘Zrtnorrgf’.

 

It’s all well and good but today our post is not about cracking a simple Crackme but about exploiting it. Wooho! Let’s get to the work.

Understanding the vulnerability

As with every exploitation challenge, it is always a good habit to check the binary for implemented security protections. We can do it with rabin2 which I demonstrated in the last post or simply by executing i from inside radare’s shell. Because we haven’t opened the binary with radare yet, we’ll go for the rabin2 method:

As you can see in the marked lines, the binary is NX protected which means that we won’t have an executable stack to rely on. Moreover, the file isn’t protected with canariespic  or relro.

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