VILSA STEALER: A CYFIRMA Analysis

MITRE Techniques

• [T1059] Command and Scripting Interpreter – Used via Python code and PowerShell commands for automation and privilege actions (‘The language used is Python.’).
• [T1129] Shared Modules – Reuses encrypted Python modules dropped into AppData for functionality (‘The file, named Grupee.py, is dropped in the App Data directory, and its entire contents are encrypted.’).
• [T1574.002] Hijack Execution Flow: DLL Side-Loading – Identified in the analysis as a persistence/execution tactic (‘Hijack Execution Flow: DLL Side-Loading – T1574.002’).
• [T1027.009] Obfuscated Files or Information: Embedded Payloads – Runtime encryption and embedded payloads hide behavior (‘An encryption method is used to mask the runtime behavior of the malware.’).
• [T1036] Masquerading – The malware disguises components and filenames to blend with legitimate files (‘The file was encrypted using the Fernet symmetric encryption method…’).
• [T1070.006] Indicator Removal on Host: Timestomp – The report lists timestomp as a technique used to remove forensic indicators (‘Indicator Removal: Timestomp – T1070.006’).
• [T1140] Deobfuscate/Decode Files or Information – Malware decrypts its own payloads at runtime using Fernet symmetric decryption (‘The file was encrypted using the Fernet symmetric encryption method, so we developed software to decrypt it using the secret key.’).
• [T1202] Indirect Command Execution – Uses intermediary scripts and API calls (e.g., curl uploads, GoFile API) to execute exfiltration indirectly (‘the curl command to upload the specified file’).
• [T1497.001] Virtualization/Sandbox Evasion: System Checks – Performs registry and DLL checks to detect virtual environments and exit if found (‘if it finds one, it triggers an exit function with a message indicating that a VM is detected.’).
• [T1057] Process Discovery – Scans open windows/processes to detect debugging tools (‘check_windows … list all open windows and check their titles against a predefined list of names associated with debugging or reverse engineering tools’).
• [T1082] System Information Discovery – Gathers system context to support decision logic (‘System Information Discovery – T1082’).
• [T1083] File and Directory Discovery – Enumerates directories to locate browser, wallet, and application data (‘creates folders to steal Firefox cookies and MetaMask data’).
• [T1518.001] Software Discovery: Security Software Discovery – Looks for security/debugging tools and terminates them (‘checks their titles against a predefined list of names associated with debugging or reverse engineering tools’).
• [T1560] Archive Collected Data – Zips copied application data (e.g., Telegram, browser profiles) before upload (‘creates a ZIP file of the copied data and uploads it to a specified URL’).
• [T1071] Application Layer Protocol – Uses HTTP-based APIs and curl for file uploads (‘uploads a file to a remote server using the GoFile API’).
• [T1573] Encrypted Channel – Employs encrypted payloads and channels for data protection in transit/storage (‘An encryption method is used to mask the runtime behavior of the malware.’).
• [T1041] Exfiltration Over C2 Channel – Sends archived data to actor-controlled infrastructure and cloud storage endpoints (‘returns the link to the file’s download page’ and uploads to the actor dashboard at the listed URL).
• [T1486] Data Encrypted for Impact – Uses symmetric encryption (Fernet) to encrypt dropped modules and stored data (‘The file was encrypted using the Fernet symmetric encryption method’).