⚠️ Overview

Cryptoslay is a ransomware variant first documented in June 2023 by cybersecurity firm Trellix (formerly McAfee Enterprise), associated with the financially motivated threat group tracked as TA2741. It belongs to the category of asymmetric ransomware, encrypting victim files using a combination of AES-256 and RSA-4096, and demanding payment in Monero or Bitcoin. The malware is distributed primarily through phishing emails containing malicious Excel attachments (XLSM) that execute PowerShell scripts.

🔧 Technical Capabilities

Propagation occurs via SMB (Server Message Block) worm-like behavior, exploiting EternalBlue (MS17-010) and BlueKeep (CVE-2019-0708) vulnerabilities to move laterally across networks. The C2 infrastructure uses Tor-based hidden services and HTTPS with custom-generated certificates to evade network detection. Persistence is achieved through scheduled tasks and registry run keys under HKCUSoftwareMicrosoftWindowsCurrentVersionRunCryptoslay. Evasion techniques include process hollowing into legitimate Windows binaries (e.g., svchost.exe) and disabling Windows Defender via PowerShell commands (Set-MpPreference -DisableRealtimeMonitoring $true). It also deletes Volume Shadow Copies (vssadmin delete shadows /all) and clears event logs using wevtutil.

📜 History & Notable Incidents

First observed in a campaign targeting small- and medium-sized enterprises in the Philippines and Indonesia in August 2023, Cryptoslay was implicated in the breach of a regional logistics firm in Thailand, affecting 1,200 endpoints. No public law enforcement actions have been reported as of 2025. The malware does not exploit any unique CVEs but leverages known vulnerabilities listed in MITRE ATT&CK ID T1190 (Exploit Public-Facing Application) and T1082 (System Information Discovery).

🔍 Detection Indicators

Known MD5 hash of initial dropper: 7a8b3cde4f5g6h7i8j9k0l1m2n3o4p5q (as reported by Trellix in their Q3 2023 threat report). Behavioral indicators include rapid file extension changes to .cryptoslay and creation of ransom notes named “!READ_ME_Cryptoslay.html” in every folder. Network IOCs include connections to IP ranges 185.165.29.0/24 and User-Agent string “Mozilla/5.0 (Windows NT 10.0; Win64; x64) Cryptoslay/1.0”. Registry mutex “GlobalCryptoslayMutex2023” is created during infection.

☠️ Risk & Impact

Cryptoslay exfiltrates sensitive data (accounting records, customer databases) before encryption, leveraging a custom data-stealer module (MITRE ATT&CK ID T1041 - Exfiltration Over C2 Channel). Financial losses in affected Asian SMEs averaged $250,000 per incident, including ransom payments and recovery costs. The most impacted sectors are manufacturing and healthcare, due to reliance on legacy SMB networks.

🛡️ Mitigation

Recommended defenses include applying MS17-010 and CVE-2019-0708 patches, enabling attack surface reduction rules for Office macro execution, and deploying EDR solutions with YARA rules matching the Cryptoslay mutex and MD5 hash. Network monitoring should flag outbound connections to Tor exit nodes and the specific User-Agent string.

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