Description

Osiris is a newly identified ransomware strain observed in a targeted intrusion against a large food-service franchisee in Southeast Asia during November 2025. Despite sharing its name with earlier malware families, this variant is assessed to be entirely new. The attack followed a well-planned intrusion lifecycle, combining data exfiltration, defense evasion, and file encryption. Notably, the operators used a bring-your-own-vulnerable-driver (BYOVD) style technique to disable security controls prior to ransomware deployment, highlighting a shift toward more kernel-level abuse in modern ransomware campaigns. From a technical perspective, attackers first staged the environment using legitimate and dual-use tools. Sensitive data was exfiltrated using Rclone to a cloud storage bucket before encryption, indicating a double-extortion strategy. The intrusion leveraged a malicious kernel driver known as POORTRY, which appears purpose-built rather than a legitimately signed but vulnerable driver. This driver was used to terminate endpoint security software and elevate privileges. Additional tooling included Netscan, Netexec, MeshAgent, KillAV, and a modified RustDesk client, while RDP was enabled to maintain remote access. The Osiris payload uses a hybrid cryptographic design combining ECC for key exchange and AES-128-CTR for per-file encryption, and it actively stops services tied to backups, databases, and productivity applications before encrypting files and dropping a ransom note. The overall impact of Osiris is considered high due to its use of kernel-level techniques, comprehensive defense evasion, and pre-encryption data theft. While the ransomware’s business model remains unclear, artifacts such as a Mimikatz variant previously associated with INC ransomware suggest possible operational overlap. Organizations running Windows environments are at risk if driver loading is not tightly controlled. Defenders should prioritize monitoring for abnormal driver installations, restrict RDP exposure, watch for abuse of tools like Rclone, and ensure secure, offline backups are maintained to reduce the impact of similar ransomware incidents.