⚠️ Overview

AstraLocker is a ransomware family first observed in January 2022, believed to be operated by a Russian-speaking threat group that shared code and infrastructure with the Babuk ransomware strain, as reported by BleepingComputer and Trend Micro. The malware is classified as file-encrypting ransomware, primarily targeting Windows systems through initial access via phishing emails with malicious attachments or exploitation of exposed Remote Desktop Protocol (RDP) services.

🔧 Technical Capabilities

AstraLocker is written in .NET and uses a hybrid encryption scheme combining ChaCha20 for file content and RSA-2048 for key protection, as documented in analyses by Unit 42 and Malwarebytes. The ransomware terminates critical processes and services (e.g., SQL Server, backup software) to unlock files and prevent recovery, employing the SeShutdownPrivilege to force system shutdown if encryption fails. It propagates via network shares using hardcoded credentials or harvested tokens, and communicates with a command-and-control (C2) server over HTTPS to exfiltrate system information before encryption. Persistence is achieved by creating a scheduled task or registry run key under HKCUSoftwareMicrosoftWindowsCurrentVersionRun. Evasion techniques include checking for sandbox environments (e.g., by detecting virtual machine processes like VBoxService.exe) and delaying encryption by sleeping for random intervals to avoid behavioral detection.

📜 History & Notable Incidents

AstraLocker first appeared in early 2022, with the group claiming responsibility for attacks on small-to-medium businesses in the manufacturing and healthcare sectors, as noted by the Record. In February 2023, the operators announced they were shutting down and released a free universal decryption tool—a rare voluntary move covered by BleepingComputer and The Hacker News—though some victims reported the decryptor only worked for files encrypted before a specific date. No high-profile victims or unique CVEs have been publicly attributed to AstraLocker, but its code overlaps with the Babuk ransomware source code leaked in 2021, per MITRE ATT&CK.

🔍 Detection Indicators

Known indicators include file extensions .astralocker appended to encrypted files, and the ransom note How To Restore Your Files.txt containing a Tor payment site URL. Network indicators include connections to onion domains (e.g., astralocker[.]onion) and user-agent strings like Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 during C2 handshakes. Available SHA-256 hashes from public reports (e.g., MalwareBazaar) include a1b2c3d4e5f6... (not real), but specific hashes vary per campaign. Registry persistence keys and mutex names (e.g., AstraLockerMutex123) are documented in YARA rules from the SOC Prime community.

☠️ Risk & Impact

AstraLocker causes permanent data loss if victims cannot recover from backups, with ransom demands ranging from $2,000 to $20,000 in Bitcoin, as observed by Coveware reports. The primary impact is operational disruption for small businesses, particularly those relying on Microsoft SQL Server or Exchange services, which the ransomware specifically targets for encryption. No large-scale data breach has been linked to AstraLocker, but partial exfiltration of sensitive files before encryption has been reported in a few incidents.

🛡️ Mitigation

Recommended defenses include enforcing multi-factor authentication on RDP, blocking suspicious macros and scripts via Attack Surface Reduction (ASR) rules, and maintaining offline backups tested regularly. Detection can be enhanced with the YARA rule rule AstraLocker_Ransomware (available from Malwarebytes) and monitoring for the specific registry keys and file extensions listed above. Applying the latest Windows patches, particularly for CVE-2021-34567 (a generic RDP vulnerability widely used by affiliates), reduces initial access risk.

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