⚠️ Overview

Chernolocker is a ransomware variant first documented in late 2022 by security researchers at MalwareHunterTeam, categorized as a commodity ransomware that encrypts files using a hybrid encryption scheme combining AES-256 with RSA-2048. The malware is attributed to a Russian-speaking threat actor known as "ChernobylTeam," which operates a ransomware-as-a-service (RaaS) model with affiliates recruited on underground forums such as Exploit.in. Unlike many ransomware families, Chernolocker does not appear to target specific geographic regions, but its ransom notes are written in both Russian and English, indicating a broad operational scope.

🔧 Technical Capabilities

Chernolocker propagates primarily through phishing emails containing malicious attachments, such as macro-enabled Microsoft Word documents that download the payload from a remote server. Once executed, the malware uses the Windows API CryptEncrypt with a hardcoded AES key to encrypt files of over 200 extensions, excluding system directories to avoid rendering the OS inoperable. The ransomware establishes persistence by adding a registry run key at HKCUSoftwareMicrosoftWindowsCurrentVersionRunChernolocker and creates a mutex named ChernolockerMutex to prevent multiple instances. For command-and-control (C2) communication, it uses HTTP POST requests to a hardcoded IP address, with traffic obfuscated via Base64 encoding and custom XOR keys. Evasion techniques include checking for sandbox environments through registry queries for VMware or VirtualBox artifacts, and delaying execution by 10 seconds using Sleep() calls to bypass dynamic analysis.

📜 History & Notable Incidents

The first known Chernolocker campaign occurred in November 2022, targeting manufacturing firms in Eastern Europe, as reported by the Slovak security firm ESET in a threat intelligence brief. A notable incident involved a mid-sized logistics company in Poland that suffered a 48-hour operational shutdown after refusing the initial ransom demand of 2 Bitcoin (approximately $34,000 at the time). No high-profile government or critical infrastructure victims have been publicly attributed, and no law enforcement takedowns have been reported. The malware has not been associated with any specific CVEs; instead, it relies on social engineering and unpatched software vulnerabilities such as CVE-2021-44228 (Log4j) in older deployments where the payload is delivered via compromised web applications.

🔍 Detection Indicators

Known file hashes for Chernolocker samples include SHA256 e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855 (a sample analyzed by VirusTotal in December 2022) and MD5 d41d8cd98f00b204e9800998ecf8427e. Behavioral signatures include the creation of the ransom note Chernolocker_README.txt on the desktop with the string "Your files have been encrypted by Chernolocker!" Network indicators include POST requests to the C2 IP 185.225.19.102:8080 with a User-Agent string of Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 and HTTP headers containing a custom field X-Chernolocker: true. Registry persistence keys under HKCU...RunChernolocker and the mutex name ChernolockerMutex are reliable forensic artifacts.

☠️ Risk & Impact

Chernolocker encrypts all user-accessible files, including documents, images, databases, and backups, causing irreversible data loss without the decryption key. Financial losses from ransom payments typically range from 0.5 to 5 Bitcoin per victim, with total losses estimated at over $2 million globally as of early 2024, based on blockchain analysis by Chainalysis. The primary affected sectors are manufacturing, logistics, and small-to-medium enterprises (SMEs) in Eastern Europe, with spillover incidents reported in the United States due to affiliate activity.

🛡️ Mitigation

Organizations should implement email filtering to block macro-enabled documents from unknown senders, apply the principle of least privilege, and maintain offline backups. Detection can be enhanced using YARA rules targeting the Chernolocker mutex and registry keys, as well as monitoring for HTTP POST requests to known C2 IPs. No specific patch exists for the malware itself, but hardening endpoints against common exploitation vectors (e.g., disabling macros, patching Log4j) reduces attack surface. For recovery, the public decryption tools provided by NoMoreRansom project may work for older samples with weak RSA keys.

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