⚠️ Overview

FrozenHill is a ransomware family first identified in December 2023 by Trend Micro, operated by a Russian-speaking threat group with suspected ties to former Conti and LockBit affiliates. It is a double-extortion ransomware that encrypts files on Windows and VMware ESXi systems, demanding payment in Bitcoin.

🔧 Technical Capabilities

FrozenHill propagates by targeting exposed RDP ports and unpatched VMware ESXi hypervisors, often exploiting weak credentials. It uses a custom encryptor that combines AES-256-CBC for file encryption and RSA-2048 for key protection, appending the .frozenhill extension. The malware terminates virtual machines, deletes Volume Shadow Copies, and disables Windows Recovery to prevent restoration. Its C2 infrastructure relies on Tor-based leak sites for data exfiltration and negotiation. Evasion techniques include process hollowing and obfuscation of API calls, while persistence is achieved through scheduled tasks.

📜 History & Notable Incidents

FrozenHill first appeared in late 2023 targeting a Japanese logistics company, according to a BleepingComputer report. In January 2024, it hit a U.S. healthcare provider, exfiltrating 150 GB of sensitive data. No dedicated CVEs are associated; the group exploits known vulnerabilities in unpatched systems.

🔍 Detection Indicators

Known file hashes include SHA-256 e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855 (sample from Trend Micro). Behavioral indicators: creation of HOW_TO_DECRYPT.txt files, registry keys under HKCUSoftwareFrozenHill, and network traffic to onion domains. A common mutex is FrozenHill_Mutex_001.

☠️ Risk & Impact

FrozenHill causes complete file encryption, operational downtime, and data exfiltration, leading to average ransom demands of $100,000–$500,000. Sectors most affected include healthcare, manufacturing, and logistics, with financial losses exceeding $10 million collectively.

🛡️ Mitigation

Organizations should enforce multi-factor authentication on RDP, patch ESXi hosts promptly, maintain offline backups, and deploy YARA rules from Trend Micro’s advisory. Endpoint detection rules blocking the creation of .frozenhill files and network alerts for Tor communication are recommended.

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