Google’s Threat Intelligence Group (GTIG), in collaboration with Mandiant, has unveiled a comprehensive analysis of ScatterBrain, an advanced obfuscation tool used by China-linked cyber espionage group APT41.
This obfuscator is central to the deployment of POISONPLUG.SHADOW, a modular backdoor targeting entities across Europe and the Asia-Pacific (APAC) region. The findings highlight ScatterBrain’s intricate design, which significantly complicates malware detection and analysis.
ScatterBrain represents a leap in obfuscation technology, evolving from earlier tools like ScatterBee.
It employs multiple sophisticated techniques to prevent both static and dynamic analysis:-
- Control Flow Graph (CFG) Obfuscation: ScatterBrain restructures the program’s control flow, scattering execution paths to confuse analysis tools.
- Instruction Mutation: Instructions are altered to obscure their true functionality without affecting program behavior.
- Complete Import Protection: The binary’s import table is encrypted and obfuscated, making it challenging to determine its interaction with the operating system.
- Dynamic Instruction Dispatchers: These disrupt CFG reconstruction by scattering execution flow and encrypting control flow branches.
- Opaque Predicates: These deceptively simple logical constructs confuse symbolic execution and disrupt path prioritization.
ScatterBrain operates in three protection modes—Selective, Complete, and Complete Headerless—with each mode offering increasing levels of complexity.
Security researchers at Google Cloud’s Mandiant detected that the most extreme, Complete Headerless, removes Portable Executable (PE) headers, introduces custom loaders, and encrypts metadata to cripple forensic analysis.
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Technical Insights into ScatterBrain’s Mechanisms
- Modes of Operation:-
- Selective: Protects specific functions within the binary while leaving others untouched.
- Complete: Applies protections across the entire binary.
- Complete Headerless: Extends the Complete mode by removing PE headers and introducing additional data encryption and custom loading mechanisms.
- Import Protection:-
ScatterBrain employs encrypted import tables where API and DLL names are hidden using a custom stream cipher. Each import is resolved dynamically via obfuscated dispatcher routines. - Control Flow Disruption:-
ScatterBrain uses instruction dispatchers to scatter execution paths. Each dispatcher dynamically calculates the next instruction block, making CFG reconstruction nearly impossible without specialized tools.
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To combat these security challenges, GTIG and Mandiant developed a standalone static deobfuscator library capable of reversing ScatterBrain’s protections.
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Key achievements include CFG recovery, which eliminates instruction dispatchers and reconstructs scattered control flows, and import table restoration, where decrypted API and DLL names help restore the operational context. Additionally, binary rewriting ensures the production of fully functional deobfuscated binaries with corrected relocations.
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The deobfuscator was tested on multiple POISONPLUG.SHADOW samples, transforming previously unintelligible binaries into fully readable executables. This breakthrough provides security analysts with critical insights into malware functionality.
GTIG’s work not only mitigates this specific threat but also sets a precedent for addressing future advancements in malware obfuscation.
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