Analysis of Raspberry Robin Malware's Functionality and Techniques
/ 4 min read
Quick take - Raspberry Robin is a complex malware characterized by its multi-layered execution process, advanced obfuscation techniques, and capabilities for evading detection while executing malicious activities and maintaining persistence on compromised systems.
Fast Facts
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Execution Layers: Raspberry Robin operates through multiple execution layers, each designed for specific tasks such as decryption, decompression, and anti-analysis, ultimately leading to its core functionality.
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Obfuscation Techniques: The malware employs advanced obfuscation methods, including control flow flattening, string obfuscation, and mixed Boolean-arithmetic operations, to evade detection and complicate analysis.
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Decoy Payload: A decoy payload is triggered in analysis environments, collecting system information (e.g., UUID, hostname) and transmitting it to a hardcoded domain, while the actual malicious activities remain concealed.
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Propagation Methods: Raspberry Robin spreads using Remote Desktop Protocol (RDP), Server Message Block (SMB), and legitimate tools like PsExec, along with techniques for UAC bypass and local privilege escalation.
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Network Communication: The malware features embedded TOR client functionality for secure communication, encrypting and relaying data to a command-and-control (C2) server, which then sends back payloads for execution.
Raspberry Robin: A Sophisticated Malware Analysis
Raspberry Robin is a sophisticated piece of malware, notable for its intricate design and advanced operational methods. A comprehensive analysis of its functionalities and obfuscation techniques has been structured into four primary sections: Execution Layers, Obfuscation Methods, Decoy Payload, and Core Layer. Each section contributes to the malware’s effectiveness in evading detection and executing malicious activities.
Execution Layers
The core functionality of Raspberry Robin is unveiled through a series of execution layers, each serving distinct purposes:
- The first execution layer employs segment registers GS/CS to detect code emulation and decrypts the subsequent layer using XOR.
- The second layer decompresses data via a modified aPLib algorithm before executing the next layer.
- The third layer evaluates CPU performance to identify analysis environments and utilizes the RC4 algorithm for decryption.
- The fourth layer decrypts the next segment using XOR.
- The fifth layer again applies the modified aPLib algorithm for decompression.
- The sixth layer implements anti-analysis techniques, triggering a decoy payload if an analysis environment is detected; if not, it decrypts the next layer using the Rabbit stream cipher.
- The seventh and eighth layers further this process by executing additional decryption and decompression steps to ultimately reach the core layer.
Recent samples of Raspberry Robin have shown an advanced capability for detecting commercial sandboxes through filename checks in the initial executable. The malware’s execution layers are designed with several anti-analysis actions, including verification of the code segment register (CS) value and resource limitations assessments through a write-combining technique.
Decoy Payload and Obfuscation Methods
The decoy payload is executed by a reflective loader without obfuscation under specific conditions. It collects vital system information, such as UUID, PEB field values, running time, hostname, and CPU name. This information is then transmitted to a hardcoded domain.
Raspberry Robin employs a variety of obfuscation techniques, including control flow flattening, bogus control flow, string obfuscation, and mixed Boolean-arithmetic operations. Each obfuscated function contains an encrypted array table for mapping variables and decrypting strings. Control flow flattening alters the execution order of conditional statements, further complicating analysis.
Core Layer and Propagation Techniques
The core layer itself integrates its own anti-analysis methods. It is capable of hiding threads and detecting virtualized environments. Its functionality is influenced by factors such as file path parameters and modified PEB fields. Additionally, Raspberry Robin ensures persistence on compromised hosts through registry keys, generating random filenames and directory names.
In terms of propagation, the malware utilizes Remote Desktop Protocol (RDP) and Server Message Block (SMB) methods. It leverages legitimate tools like PsExec and PAExec, and employs User Account Control (UAC) bypass techniques and local privilege escalation exploits to enhance its permissions. Moreover, Raspberry Robin verifies connectivity to the TOR network, incorporating embedded TOR client functionality for secure network communication. The malware encrypts and relays collected data to a command-and-control (C2) server, which subsequently responds with payloads executed in new threads.
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