The Power of Binary Diffing in Malware Analysis

In the ever-evolving landscape of cybersecurity, malware analysis remains a critical skill for defenders. While many are familiar with static and dynamic analysis techniques, Binary Diffing is a lesser-known yet powerful method that can provide deep insights into malware behavior and evolution. In this blog, we’ll explore what binary diffing is, how it works, and demonstrate its application with practical examples.

What is Binary Diffing?

Binary diffing is a technique used to compare two or more binary files to identify differences between them. This method is particularly useful in malware analysis to:

• Track changes in malware versions.
• Identify new functionalities or evasion techniques.
• Understand patch differences in software vulnerabilities.

Unlike traditional methods that focus on the behavior or structure of a single binary, binary diffing allows analysts to contextualize changes over time or across variants.

How Does Binary Diffing Work?

Binary diffing involves comparing the binary code of two files at a low level. Tools like BinDiff, Diaphora, and Radare2 are commonly used for this purpose. These tools analyze the binary’s assembly code, control flow, and function signatures to highlight differences.

Here’s a simple breakdown of the process:

1. Disassemble the Binaries: Convert the binary files into assembly code.
2. Compare Functions: Identify matching and non-matching functions between the binaries.
3. Analyze Changes: Examine differences in instruction sets, control flow, and data structures.
4. Contextualize Findings: Relate the changes to potential updates in malware behavior or evasion techniques.

Practical Example: Analyzing a Ransomware Variant

Let’s dive into a practical example to understand binary diffing better. Suppose we have two versions of a ransomware binary: Ransomware_v1.exe and Ransomware_v2.exe. Our goal is to identify the changes introduced in the second version.

Step 1: Disassemble the Binaries

We’ll use Radare2 to disassemble both binaries. Here’s the command to disassemble Ransomware_v1.exe:

r2 -A Ransomware_v1.exe

Repeat the same for Ransomware_v2.exe.

Step 2: Compare Functions

Using BinDiff, we load both disassembled binaries and compare their functions. BinDiff highlights changes in function names, instruction sets, and control flow. For example, we might notice that a function named EncryptFiles in Ransomware_v1.exe has been replaced with EncryptFilesV2 in Ransomware_v2.exe.

Step 3: Analyze Changes

Upon closer inspection, we find that EncryptFilesV2 includes additional instructions for anti-debugging techniques. This suggests that the malware authors are trying to evade analysis tools in the updated version.

Step 4: Contextualize Findings

The introduction of anti-debugging techniques in Ransomware_v2.exe indicates a deliberate effort by the attackers to make analysis more challenging. This insight can help defenders update their tools and techniques to counter the new evasion methods.

Advanced Techniques in Binary Diffing

While basic binary diffing is powerful, advanced techniques can provide even deeper insights:

• Cross-Architecture Diffing: Compare binaries compiled for different architectures (e.g., x86 vs. ARM).
• Symbolic Execution: Use symbolic execution to understand how differences in binary code affect program behavior.
• Machine Learning: Apply machine learning algorithms to classify and predict changes in malware families.

Challenges in Binary Diffing

Despite its advantages, binary diffing has its challenges:

• Code Obfuscation: Malware authors often obfuscate their code, making it harder to identify changes.
• False Positives: Differences in compiler optimizations can lead to false positives.
• Scalability: Comparing large binaries or multiple variants can be resource-intensive.

Conclusion

Binary diffing is a powerful yet underutilized technique in malware analysis. By comparing binary files, analysts can uncover hidden changes, understand malware evolution, and develop effective countermeasures. While it comes with its challenges, the insights gained from binary diffing make it an invaluable tool in the cybersecurity arsenal.

Whether you’re a seasoned malware analyst or just starting out, mastering binary diffing can give you a significant edge in the fight against cyber threats.

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