How do you analyze encrypted malware payloads without executing them?

First, you check all of the behavioral patterns of the malware using things like FakeDNS, hashes, strings, and Ghidra (or similar) to crack open the code and examine it. That said, eventually you do execute them - you just do so in a safe environment with layers and layers of protection on multiple fronts.

Understanding the landscape in which malware operates, such as the execution environment, can provide valuable insights into possible objectives and evasion methods. Monitoring trends in cyber threats is also critical to continually adjust analysis strategies as attackers respond quickly to changes in security defenses.

During a recent malware analysis engagement, I encountered a custom encryption algorithm hidden within an executable. The malware was designed to evade detection by using XOR encryption. To identify this, I used a combination of PEiD and Detect It Easy, which hinted at the use of XOR due to specific patterns in the binary code. Further analysis with a hex editor revealed repeating byte sequences, a hallmark of XOR encoding. Identifying the encryption type early on was critical because it allowed me to move forward with the decryption process quickly, saving time and preventing the malware from causing further damage.

The first step is to determine if the binary is encrypted or encoded. One way of doing this would be to analyze the entropy of the binary section of the executable which can be done with certain hex editors. Assuming encoding is used, the payload is much easier to decode. Regardless of this step, you will eventually need to perform static analysis on the binary. Using this and the knowledge gained during static analysis you can then decrypt the binary data using a script you would then need to write. Unfortunately, doing this entirely through static analysis can sometimes be difficult. Some payloads choose to brute force a key at runtime such as veil. In these cases, you would have to brute force it with an external script.

To identify the encryption type used in encrypted malware payloads, you can utilize tools like PEiD, Detect It Easy, or CFF Explorer to analyze the executable file for signatures, headers, sections, imports, and exports. Additionally, inspecting the binary code with a hex editor or disassembler can reveal patterns, constants, or keys that indicate the encryption method, whether it's symmetric, asymmetric, XOR, Base64, or a custom algorithm. Recognizing these clues helps determine the encryption type, essential for further analysis and decryption efforts.

I think the easiest way to extract the "encrypted" payload is to go about mapping and extracting the binary data based on what type of file it is. This will be different depending on the platform. Then extract the binary data from whatever happens to be encrypted. Obviously this depends on what was used. Some packers might have unpackers, but is sometimes not the only way. You can sometimes pause execution of the malware right after the malware decrypts itself. Then dump the memory at this location.

Extracting the encrypted payload from malware involves careful analysis to understand its structure and encryption method. Through static analysis, security experts inspect the malware file's code, identifying encryption algorithms, keys, and patterns. Memory analysis tools may reveal the payload in its decrypted state while residing in the system's memory during execution. Sandboxing and controlled environments help observe the payload's behavior without executing it, offering insights into potential decryption processes. Advanced techniques, such as API monitoring and traffic analysis, provide additional avenues to extract encrypted payloads' characteristics.

To extract the encrypted payload from an executable file, you can use various tools and techniques based on the encryption type and packing method. Common packers like UPX, ASPack, or PECompact can be unpacked using UPX, PECompact, or PE Explorer. Debuggers such as OllyDbg, x64dbg, or Immunity Debugger can attach to the executable and dump memory regions containing the payload. Alternatively, file carving tools like Binwalk, Foremost, or HxD can extract the encrypted payload based on file signatures or offsets.

To decrypt an encrypted payload, first identify the encryption type. For XOR-encoded payloads, use tools like XORSearch, XORBruteForcer, or CyberChef to brute-force or guess the key. For Base64-encoded, AES-encrypted, or RSA-encrypted payloads, use appropriate tools like Base64 Decoder, AES Decryptor, or RSA Decryptor, providing the necessary key or passphrase. If the encryption algorithm is unknown, use reverse engineering tools like IDA Pro, Ghidra, or Radare2 to analyze and implement the decryption algorithm in a scripting language.

Decrypting the encrypted payload entails employing appropriate tools and techniques based on encryption type and key availability. For XOR-encoded payloads, options like XORSearch or XORBruteForcer facilitate decryption via brute-force or key approximation. Decryption of Base64-encoded, AES-encrypted, or RSA-encrypted payloads requires tools like Base64 Decoder, AES Decryptor, or RSA Decryptor, with the key or passphrase provided. Alternatively, decrypting algorithms via reverse engineering using tools like IDA Pro or Ghidra, and implementing them in scripting languages like Python, Ruby, or Perl, offers an intricate yet effective approach.

To analyze a decrypted payload, begin by scanning it with tools like VirusTotal, PEStudio, or Malwarebytes to check for malware signatures and indicators of compromise. Examine its structure and metadata using PEView, Resource Hacker, or Exeinfo PE. For deeper analysis, disassemble and decompile the code with IDA Pro, Ghidra, or Radare2 to understand its logic and behavior. Each tool offers specific insights into the payload's characteristics, helping to identify and mitigate potential threats.

Analyzing the decrypted payload is the final crucial step, necessitating adept utilization of tailored tools and techniques. Depending on payload type and functionality, diverse methods may be employed. Tools like VirusTotal, PEStudio, or Malwarebytes enable scanning for malware signatures, indicators of compromise, or malicious behavior. Alternatively, tools such as PEView, Resource Hacker, or Exeinfo PE facilitate analysis of payload structure, resources, or metadata. For a deeper understanding, disassembling and decompiling the payload code using tools like IDA Pro, Ghidra, or Radare2 unveils its logic, flow, and purpose, ensuring comprehensive analysis and informed decision-making.

It’s critical to do malware analysis in a safe setup. Some malware can detect if it’s in a VM sandbox, so having a realistic network lab is best, though it can be pricey. Even for simpler malware, stick to a dedicated machine or sandboxed environment. Tools like Ghidra on REMnux, Kali, or Windows work well for static analysis. Wireshark and ProcMon are also great for seeing what malware does in real time.

In addition to relying on conventional tools such as PEiD, Detect It Easy, and CFF Explorer, it is recommended to incorporate more proactive approaches in malware analysis. This includes exploring machine learning techniques to identify unconventional patterns and subtle variations that may go unnoticed by traditional methods. Training these models with diverse datasets can strengthen detection capabilities in the face of custom encryption and more sophisticated methods.