Ransom:Win32/Medusa.PA!MTB

The Ransom:Win32/Medusa.PA!MTB ransomware operates as a Windows Portable Executable, initiating a deliberate sequence of actions upon launch. It begins by conducting reconnaissance of the local and accessible network file systems to identify target data for encryption. The encryptor processes files, appending the distinctive .MEDUSA extension while employing a built-in exclusion list to bypass critical Windows directories such as \Windows\ and \Program Files\ and to ignore specific file types including binaries (.exe) and dynamic-link libraries (.dll). This selective avoidance helps maintain system stability to ensure the ransom note remains visible. Threat actors can influence this process through command-line parameters; for example, using the -d flag prevents the binary from self-deleting, while the -t flag allows specification of a custom ransom note filename.  

Prior to the encryption routine, the payload runs disruptive commands to eliminate recovery options. It issues a series of net stop commands targeting a predefined list of services, particularly those associated with endpoint security (Sophos, McAfee), backup software (Veeam, Acronis VSS Provider), and database servers (MSSQLSERVER). It also uses taskkill to terminate related processes. To further cripple restoration efforts, it invokes vssadmin delete shadows /all /quiet to destroy Volume Shadow Copies. Following encryption, Medusa deposits its ransom note, titled !!!READ_ME_MEDUSA!!!.txt, on the user's desktop and within each affected folder. 

For persistence, Medusa modifies the Windows registry, creating a key named MDSLK within HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run. This ensures the malicious payload runs every Windows startup. Medusa uses living-off-the-land techniques for evasion, embedding its activities within legitimate Windows processes. Documented instances show the use of certutil.exe to decode auxiliary files and the execution of complex, multi-stage PowerShell scripts. One such script employs a base64-encoded and gzip-compressed payload that is decompressed and loaded into memory; a tactic designed to avoid leaving forensic artifacts on disk. It also attempts to obscure these actions by clearing PowerShell command history. During incidents, additional tooling is often observed. For instance, a batch file named openrdp.bat (MD5: 44370f5c977e415981febf7dbb87a85c) is used to modify firewall rules and open inbound Remote Desktop Protocol connections, while a utility like pu.exe (MD5: 80d852cd199ac923205b61658a9ec5bc) may provide a reverse shell for operator access. 

The malware has been observed communicating with command-and-control infrastructure at IP addresses including 207[.]188.6[.]17, 172[.]64.154[.]227, 103[.]217.41[.]10, and 194[.]28.50[.]70. It also contacts domains such as gosw602.adventos[.]de. Data exfiltration and ransom negotiation frequently involve email addresses like key.medusa.serviceteam@protonmail[.]com and medusa.support@onionmail[.]org. The operation maintains a public data-leak site on the Tor network for double extortion. File hashes for captured samples, such as SHA-256 4d4df87cf8d8551d836f67fbde4337863bac3ff6b5cb324675054ea023b12ab6 and 657c0cce98d6e73e53b4001eeea51ed91fdcf3d47a18712b6ba9c66d59677980, serve as definitive fingerprints for detection.