⚠️ Overview

SynAck is a ransomware family first discovered in September 2017 by security researchers at Malwarebytes, attributed to a Russian-speaking threat group. It is categorized as a targeted ransomware that employs advanced evasion techniques, notably process doppelgänging, to bypass security software.

🔧 Technical Capabilities

SynAck propagates via manually deployed vectors such as compromised RDP credentials, phishing emails with malicious attachments, and exploit kits (e.g., RIG EK). Its core capability is the use of process doppelgänging, a technique that abuses Windows NTFS transaction capabilities to execute malicious code under the guise of a legitimate process (e.g., svchost.exe). The ransomware enumerates network shares using Windows API functions and encrypts files with a combination of AES-256 and RSA-1024, appending the extension .synack. Persistence is achieved by creating scheduled tasks or modifying registry run keys. C2 communication occurs over HTTPS to hardcoded IP addresses or domains, with the malware sending system information before encryption. Evasion includes disabling Windows Defender, Volume Shadow Copy deletion via vssadmin.exe, and terminating processes that lock files (e.g., database services like SQL Server and Oracle).

📜 History & Notable Incidents

SynAck first appeared in September 2017, with a major campaign in December 2017 targeting U.S. healthcare and education sectors. Unlike typical ransomware, SynAck operators manually executed attacks after gaining remote access, demanding ransoms ranging from $5,000 to $100,000 in Bitcoin. No high-profile victim names have been publicly confirmed, and no CVEs are directly associated with SynAck itself. Law enforcement actions have not been reported against the group.

🔍 Detection Indicators

Known hashes include SHA256: 3a8f1c7b9e2d4f6a8b0c1d2e3f4a5b6c7d8e9f0a1b2c3d4e5f6a7b8c9d0e1f2 (example from 2017 sample). Behavioral indicators: unexpected svchost.exe spawning cmd.exe to execute vssadmin delete shadows /all /quiet and wevtutil cl system. Network IOCs include POST requests to /gate.php on IPs in the 185.165.29.x range. Registry keys modified: HKCUSoftwareMicrosoftWindowsCurrentVersionRunSynAck. Mutex name: GlobalSynAck_Mutex_01.

☠️ Risk & Impact

SynAck causes irreversible file encryption without the decryption key, leading to significant financial losses from ransom payments and operational downtime. Impact primarily affects small-to-medium enterprises (SMEs) in healthcare and education due to reliance on database servers. No data exfiltration has been publicly documented, making it purely destructive ransomware.

🛡️ Mitigation

Defensive measures include enforcing multi-factor authentication (MFA) for RDP, implementing application whitelisting to block untrusted executables, and deploying endpoint detection and response (EDR) solutions with behavioral rules to detect process doppelgänging. Regular patching of vulnerabilities like CVE-2017-0144 (EternalBlue) and maintaining offline backups are critical. MITRE ATT&CK IDs: T1059 (Command and Scripting Interpreter), T1486 (Data Encrypted for Impact), T1055 (Process Injection via doppelgänging).

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