Analysis of Encryption Structure of Yurei Ransomware Go-based Builder

Yurei ransomware, identified in September 2025, targets corporate networks primarily in transportation, IT, marketing, and food sectors. Developed in Go, it uses strong encryption algorithms ChaCha20-Poly1305 for file encryption and secp256k1-ECIES for key protection. The ransomware excludes certain files and directories to maintain system operability. Each file is encrypted with a unique key and nonce, ensuring only the attacker can decrypt the data. The ransom note threatens data leaks and regulatory notifications if demands are unmet within five days. While currently observed in Sri Lanka and Nigeria, the ransomware’s sophisticated encryption and typical corporate targeting pose a medium-level threat globally. No known exploits in the wild or CVEs exist yet. European organizations should be vigilant due to potential expansion and regulatory impact. Mitigation requires proactive network segmentation, strict access controls, and advanced detection of lateral movement and privilege escalation.

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