Challenge Overview

A user on your network has reported that their important documents, specifically within a folder named **CTF_Vault**, have been encrypted by **ransomware**. A ransom note is displayed demanding payment. You, as a security analyst, have obtained a copy of the malware file. Your task is to analyze this malware, figure out how the encryption works, find the decryption key, and recover the user's files (specifically the flag contained within **Flag.txt**). The target executable ransomware is a.NET application that has been packed using a.NET packer. This means the initial executable primarily serves to load and execute the real ransomware code hidden within it. The challenge requires unpacking the executable using dynamic analysis (debugging), then performing static analysis on the unpacked payload to understand the key generation mechanism. The ransomware uses AES encryption, and the key is derived from the victim machine's hostname. By completing this challenge, you will learn about unpacking packed.NET executables, analyzing.NET code for cryptographic keys, and using debugging tools like dnSpy.

What You Will Learn

  • Understanding the behavior and impact of ransomware targeting user files.
  • Unpacking a packed .NET executable using dynamic analysis and debugging techniques.
  • Performing static analysis on the unpacked malware to understand its functionality.
  • Identifying how AES encryption is implemented and how the key is generated.
  • Recovering encrypted files by deriving the decryption key from the system\\u2019s hostname.

Program Curriculum

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