Gentlemen is a ransomware-as-a-service family first observed in mid-2025 that combines advanced encryption with worm-like propagation to maximize impact in Windows environments. Written in Go and obfuscated with Garble, it primarily targets organizations in the education, healthcare, transportation, and financial sectors across multiple regions. The operators also conduct double-extortion by stealing sensitive data before encryption and threatening to publish it if victims refuse to pay. Encrypted files receive the .umc16h extension and a README-GENTLEMEN.txt ransom note. Its hybrid cryptographic design uses Curve25519 and XChaCha20, generating a unique ephemeral key pair for every file, making unauthorized decryption highly difficult. The ransomware begins execution only after validating an operator-supplied password. With elevated execution options, it creates scheduled tasks to relaunch itself as SYSTEM, gaining higher privileges. Before encrypting files, it disables Microsoft Defender, adds antivirus exclusions, deletes Volume Shadow Copies, clears Windows logs, removes PowerShell histories, and terminates backup, database, virtualization, and endpoint security services to prevent recovery and detection. Persistence is maintained through scheduled tasks and Windows Run registry keys, while file ownership and permissions are modified to guarantee unrestricted access during encryption. Its most distinctive feature is a worm-like propagation module copying malware to C:\Temp, creates a hidden SMB share, deploys PsExec, and scans for reachable systems. It remotely disables Defender and Windows Firewall, enables SMB1, and weakens anonymous-access restrictions before attempting up to 21 remote execution methods, including PsExec, WMIC, scheduled tasks, services, PowerShell remoting, and WMI. During encryption, each file is protected using a newly generated Curve25519 key pair and XChaCha20, with the ephemeral public key appended to the file footer for later decryption. Gentlemen highlights the growing sophistication of modern ransomware through strong cryptography, automated privilege escalation, defense evasion, and resilient lateral movement. Organizations should implement least-privilege access, network segmentation, disable SMB1, restrict remote administration tools, maintain offline backups, enable behavior-based endpoint detection, and continuously monitor for suspicious PowerShell activity, credential misuse, and mass file encryption to contain attacks before they spread.
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