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



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.



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.

Continue reading

Fantastic Malware and Where to Find Them


We, as malware analysts, are always in need of new samples to analyze in order to learn, train or develop new techniques and defenses. One of the most common questions I get is “Where to find malware to analyze?” so I’m sharing here my private collection of repositories, databases and lists which I use on a daily basis. Some of them are updated frequently and some of them are not. The short description under each link wasn’t written by me, it was written by the owners of the repositories.

If you want to add another resource to the list please inform me in the comments.

Please, be careful when using these sites. Almost all of them contain malicious files. Use with caution!

General Samples

theZoo is a project created to make the possibility of malware analysis open and available to the public.

Contagio is a collection of the latest malware samples, threats, observations, and analyses.

Hybrid Analysis
Free malware analysis service powered by Payload Security. Using this service you can submit files for in-depth static and dynamic analysis. You can also download samples from analysis submitted by others.

AVCaesar is a malware analysis engine and repository, developed by

Das Malwerk
DAS MALWERK collects executable malware from all kinds of shady places on the internet
An active community devoted to malware analysis and kernel development

The MalShare Project is a collaborative effort to create a community-driven public malware repository that works to build additional tools to benefit the security community at large.



VirusBay is a web-based, collaboration platform where researchers can put their hands on malicious samples uploaded by colleagues and SOC professionals.

FreeTrojanBotnet’s goal is to gather submissions from operators and various mailing lists and concentrate them in a database easy to navigate

Virusign downloads malware and sort files in order of relevance, for researchers to download samples and analyze them to create new signatures.
A binary substring searchable malware catalog containing terabytes of malicious code. (Samples are not downloadable)

A repository of malware samples to provide security researchers, incident responders, forensic analysts, and the morbidly curious access to samples of malicious code.

Malwarebytes Research Center
Forums to post new threats and URLs

Mobile Malware (Google Group)
A mailing list for researching mobile malware. This group allows material related to new mobile malware samples, analysis, new techniques, questions pertaining to the field, and other related material.

Search And RetrieVAl of Malware contains a database with tons of malicious samples.

Malekal’s collection of malware

An updated database of domains hosting malicious executables.

VX Vault
S!Ri.URZ Collection of malware and URLs

Providing access to a database which contains data such as: URL, MD5, IP, TLD, etc

Sucuri Malware Labs
Latest findings that Sucuri Labs seeing in the “wild” is running a couple of projects helping internet service providers and network operators protecting their infrastructure from malware. It includes several malware trackers.

Cybercrime Tracker
Lists the C&C panels of certain in-the-wild botnets.

Android Samples

Koodous is a collaborative platform that combines the power of online analysis tools with social interactions between the analysts over a vast APKs repository.

AndroMalShare is a project to share Android malware samples

Android-Malware (Github)
Collection of Android malware samples collected from several sources/mailing lists

OSX Samples

Objective-See Mac Malware
Objective-See was created to provide simple, yet effective OS X security tools. Always free of charge. This repository contains malware samples for MAC.

Manwe MAC Malware Samples
Regularly updated fresh MAC malware feed

Linux Samples

Linux Sandbox
Linux Sandbox is a Cuckoo-based sandboxing system specifically crafted and tuned for Linux malware samples analysis.

Detux – The Linux Sandbox
Multiplatform Linux Sandbox. The samples are available to download.

Not working anymore or under maintenance:

Open Malware Project by Danny Quis

Malwr is a free malware analysis service and community launched in January 2011. You can submit files to it and receive the results of a complete dynamic analysis back. You can also download samples from analysis submitted by others.

Repository of Malware URLs and Samples


Again, please be careful when using these sites. Almost all of them contain malicious files. Use with caution!