The Anubis Backdoor, a Python-based malware, was recently uncovered as part of an advanced toolset used by the notorious cybercrime group FIN7. Active since at least 2015, FIN7 has targeted various industries, particularly financial institutions and hospitality sectors, causing billions of dollars in damages globally. The discovery of Anubis marks a significant evolution in FIN7’s tactics, with this new tool blending seamlessly into legitimate system operations, making detection increasingly difficult. The backdoor leverages Python, a versatile language, to operate stealthily on compromised systems while granting attackers remote access for further exploitation.
This sophisticated backdoor is primarily spread through phishing campaigns, with attackers using a ZIP archive containing obfuscated Python scripts to deliver their payload.
The key script, named “conf.py,” employs advanced obfuscation techniques such as AES encryption in CBC mode, SHA-256 hashing, and Base64 encoding to hide the malicious code. The script decrypts the payload, writes it to a temporary file, executes it, and deletes the file to minimize its footprint on the system. These multi-layered techniques ensure the backdoor remains hidden from traditional detection methods, complicating any analysis or remediation efforts.
Once installed, the Anubis Backdoor allows attackers to establish persistent communication with the compromised system via HTTP ports (80/443).
This method of communication blends the malware’s traffic with regular network activity, further evading detection. To maintain long-term access, the backdoor stores its command-and-control (C2) configuration in the Windows Registry, encrypted with AES-CBC using a unique key derived from the agent ID and the victim’s computer name. This encryption ensures each infection is unique, making it harder for security researchers to decrypt and analyze without specific knowledge of the environment. Additionally, the backdoor can upload and execute additional malware, providing attackers with flexibility to expand their control over the infected systems.
The Anubis Backdoor exemplifies FIN7’s growing sophistication in malware development. With advanced techniques such as multi-layered obfuscation, encryption, and modular command structures, the backdoor offers attackers significant capabilities, including full shell access, dynamic control over C2 infrastructure, and the ability to exfiltrate sensitive data. The persistent and stealthy nature of the backdoor, coupled with its ability to operate covertly across Windows environments, demonstrates FIN7’s commitment to evolving its cybercriminal tactics.
