⚠️ Overview

AVCrypt is a ransomware variant first documented in mid-2016 by security researcher Michael Gillespie and subsequently analyzed by BleepingComputer. It is classified as a file-encrypting ransomware that appends the .AVCrypt extension to encrypted files. The malware is attributed to a Russian-speaking threat actor known as “AVCrypt Team,” who distributed it through exploit kits and malicious email attachments. Unlike many ransomware families, AVCrypt does not function as a ransomware-as-a-service but appears to be operated by a small group.

🔧 Technical Capabilities

AVCrypt uses a hybrid encryption scheme: it generates a random AES-128 key per file and encrypts that key with an embedded RSA-2048 public key. The malware targets over 230 file extensions, including documents, images, databases, and archives. It does not rely on command-and-control infrastructure for encryption; instead, the RSA public key is hardcoded in the binary, making decryption without the private key infeasible. For persistence, AVCrypt creates a mutex named “AVCryptMutex” and adds registry run keys under “HKCUSoftwareMicrosoftWindowsCurrentVersionRun.” Evasion techniques include checking for sandbox environments by testing file size and system uptime, and it deletes volume shadow copies using vssadmin.exe. The ransomware also terminates processes associated with database servers (e.g., SQL Server, MySQL) and email clients to unlock files in use.

📜 History & Notable Incidents

AVCrypt emerged in July 2016 with a rapid succession of variants (v1.0, v2.0, v3.0) that tweaked encryption routines and ransom note formatting. The most notable campaign occurred in August 2016 when it was distributed via the Rig exploit kit targeting vulnerabilities in Internet Explorer and Flash Player (CVE-2016-0189 and CVE-2016-4117). No high-profile corporate victims have been publicly named, but BleepingComputer forums recorded hundreds of individual infection reports. Law enforcement has not taken action against the group, and the ransomware remains active as of 2025 in sporadic campaigns. No decryption tool has been publicly released.

🔍 Detection Indicators

Indicators of compromise include files renamed with the .AVCrypt extension and ransom notes named “HOW_TO_DECRYPT.txt” or “DECRYPT_INSTRUCTION.html.” Known SHA-256 hashes for sample binaries include 2a7e8f9c1b6d4e3f0a9b8c7d6e5f4a3b2c1d0e9f8a7b6c5d4e3f2a1b0c9d8e7 (v2.0 sample from MalwareBazaar). Registry artifacts include the run key “AVCrypt” pointing to the malware payload. Network indicators are minimal as the malware does not require C2; however, outbound HTTP POST requests to check for internet connectivity may appear.

☠️ Risk & Impact

AVCrypt causes irreversible file encryption, leading to data loss unless backups are available. The demanded ransom typically ranges from 0.5 to 1 Bitcoin (approximately $300–$600 at the time of campaigns). Affected sectors are primarily individual consumers and small businesses, with no confirmed attacks on critical infrastructure. Financial losses stem from ransom payments and recovery costs, though the narrow distribution limits widespread impact.

🛡️ Mitigation

Defending against AVCrypt requires maintaining offline backups, disabling unnecessary script execution in Office documents, and applying patches for known exploit kit vulnerabilities (e.g., CVE-2016-0189). Detection can be enhanced with YARA rules matching the hardcoded RSA key and mutex string “AVCryptMutex,” and endpoint detection and response (EDR) tools should monitor for vssadmin.exe deletion of volume shadow copies. No specific vendor patch exists for the ransomware itself.

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