McAfee ATR Analyzes Sodinokibi aka REvil Ransomware-as-a-Service

Episode 1: What the Code Tells Us

McAfee’s Advanced Threat Research team (ATR) observed a new ransomware family in the wild, dubbed Sodinokibi (or REvil), at the end of April 2019. Around this same time, the GandCrab ransomware crew announced they would shut down their operations. Coincidence? Or is there more to the story?
In this series of blogs, we share fresh analysis of Sodinokibi and its connections to GandCrab.

- Episode 1: What the Code Tells Us

- Episode 2: The All-Stars

- Episode 3: Follow the Money

- Episode 4: Crescendo

In this first installment we share our extensive malware and post-infection analysis and visualize exactly how big the Sodinokibi campaign is.

Background

Since its arrival in April 2019, it has become very clear that the new kid in town, “Sodinokibi” or “REvil” is a serious threat. The name Sodinokibi was discovered in the hash ccfde149220e87e97198c23fb8115d5a where ‘Sodinokibi.exe’ was mentioned as the internal file name; it is also known by the name of REvil.

At first, Sodinokibi ransomware was observed propagating itself by exploiting a vulnerability in Oracle’s WebLogic server. However, similar to some other ransomware families, Sodinokibi is what we call a Ransomware-as-a-Service (RaaS), where a group of people maintain the code and another group, known as affiliates, spread the ransomware.

This model allows affiliates to distribute the ransomware any way they like. Some affiliates prefer mass-spread attacks using phishing-campaigns and exploit-kits, where other affiliates adopt a more targeted approach by brute-forcing RDP access and uploading tools and scripts to gain more rights and execute the ransomware in the internal network of a victim. We have investigated several campaigns spreading Sodinokibi, most of which had different modus operandi but we did notice many started with a breach of an RDP server.

Who and where is Sodinokibi hitting?

Based on visibility from MVISION Insights we were able to generate the below picture of infections observed from May through August 23rd, 2019:

Who is the target?

Mostly organizations, though it really depends on the skills and expertise from the different affiliate groups on who, and in which geo, they operate.

Reversing the CodeIn this first episode, we will dig into the code and explain the inner workings of the ransomware once it has executed on the victim’s machine.

Overall the code is very well written and designed to execute quickly to encrypt the defined files in the configuration of the ransomware. The embedded configuration file has some interesting options which we will highlight further in this article.

Based on the code comparison analysis we conducted between GandCrab and Sodinokibi we consider it a likely hypothesis that the people behind the Sodinokibi ransomware may have some type of relationship with the GandCrab crew.

Inside the codeSodinokibi Overview

The main goal of this malware, as other ransomware families, is to encrypt your files and then request a payment in return for a decryption tool from the authors or affiliates to decrypt them.

The malware sample we researched is a 32-bit binary, with an icon in the packed file and without one in the unpacked file. The packer is programmed in Visual C++ and the malware itself is written in pure assembly.

Technical DetailsThe goal of the packer is to decrypt the true malware part and use a RunPE technique to run it from memory. To obtain the malware from memory, after the decryption is finished and is loaded into the memory, we dumped it to obtain an unpacked version.

The first action of the malware is to get all functions needed in runtime and make a dynamic IAT to try obfuscating the Windows call in a static analysis. The next action of the malware is trying to create a mutex with a hardcoded name. It is important to know that the malware has 95% of the strings encrypted inside. Consider that each sample of the malware has different strings in a lot of places; values as keys or seeds change all the time to avoid what we, as an industry do, namely making vaccines or creating one decryptor without taking the values from the specific malware sample to decrypt the strings.

Code Comparison with GandCrab

Using the unpacked Sodinokibi sample and a v5.03 version of GandCrab, we started to use IDA and BinDiff to observe any similarities. Based on the Call-Graph it seems that there is an overall 40 percent code overlap between the two:

The most overlap seems to be in the functions of both families. Although values change, going through the code reveals similar patterns and flows:

Although here and there are some differences, the structure is similar:

We already mentioned that the code part responsible for the random URL generation has similarities with regards to how it is generated in the GandCrab malware. Sodinokibi is using one function to execute this part where GandCrab is using three functions to generate the random URL.

Where we do see some similar structure is in the parts for the to-be-generated URL in both malware codes. We observe how even though the way both ransomware families generate the URL might differ, the URL directories and file extensions used have a similarity that seems to be more than coincidence. This observation was also discovered by Tesorion in one of its blogs.

Overall, looking at the structure and coincidences, either the developers of the GandCrab code used it as a base for creating a new family or, another hypothesis, is that people got hold of the leaked GandCrab source code and started the new RaaS Sodinokibi.

Conclusion

Sodinokibi is a serious new ransomware threat that is hitting many victims all over the world.

We executed an in-depth analysis comparing GandCrab and Sodinokibi and discovered a lot of similarities, indicating the developer of Sodinokibi had access to GandCrab source-code and improvements. The Sodinokibi campaigns are ongoing and differ in skills and tools due to the different affiliates operating these campaigns, which begs more questions to be answered. How do they operate? And is the affiliate model working? McAfee ATR has the answers in episode 2