AsyncRAT is an open source remote administration tool written in C#. It is often used by attackers for malicious purposes. It contains obfuscated and AES-encrypted strings in its configuration. In this blog post, I would like to describe my approach of decrypting those strings with CyberChef with leverage the power of Registers and other CyberChef features.
Attackers compromised up to 1500 companies during massive ransomware attack, which is now reported as one of the largest cyber attacks ever. Victims have been infected with REvil ransomware, which is similar to DarkSide ransomware used recently in Colonial Pipeline attack. However, this time, the deployed REvil ransomware was more obfuscated than versions observed in beginning of 2021. In this article, we will discuss the obfuscation techniques used by REvil in Kaseya incident.
Introduction In the post about GandCrab String Decryption I use very simple heuristic for identifying the function for string decryption. Because this kind of funtion is usually heavily used, I made an assumption that the scting decryption function is the most used function in our sample. This assumption is correct for GandCrab v5.1 DLL files, but it turns out that it is not true for GandCrab v5.2 and v.53. EXE samples.
Introduction In the last arcitle about Ursnif campaign have been presented the ursnif powershell downloader, which was also able to download the GandCrab payload. This payload was injected as DLL library into the running process and during the last analysis I have extracted it. Now, it is time to look more closely at this GandCrab sample. Obfuscated strings After a quick look at the disassembly we can notice many calls to one particular function, in our case named by IDA as sub_10009E69.
Introduction In the first part of this analysis have been presented the two types of macro-enabled documents with powershell downloader spreading via emails in recent campaign. The powershell downloaders and/or the macros were slightly obfuscated, however, it was easy to defeat this obfuscation and reveal their purpose. Unfortunately, during my analysis the downloaded content was not present on the involved servers and also in the most cases it was not available even during the analysis on sandboxes like Any.