A newly observed Kyber ransomware campaign is targeting both Windows systems and VMware ESXi environments, showing a coordinated effort to maximize disruption across enterprise networks. Security researchers at Rapid7 identified two separate variants during a March 2026 incident response, both deployed within the same compromised infrastructure. One variant is tailored specifically for ESXi hypervisors, while the other focuses on Windows-based servers. The ESXi version is designed for virtualization environments, enabling attackers to enumerate virtual machines, encrypt datastore files, and optionally terminate running VMs. It also defaces ESXi management interfaces with ransom instructions, increasing pressure on victims. Despite claims of using post-quantum encryption via Kyber1024, this variant actually relies on conventional cryptography—ChaCha8 for file encryption and RSA-4096 for securing keys. File encryption behavior varies by size, with smaller files fully encrypted and larger ones partially or intermittently encrypted based on attacker settings. In contrast, the Windows variant, developed in Rust, is more advanced and aligns more closely with its claims. It uses Kyber1024 alongside X25519 to protect encryption keys, while AES-CTR is used for encrypting data. This demonstrates a hybrid approach where post-quantum methods secure key exchange rather than encrypt files directly. The malware aggressively disrupts recovery efforts by deleting backups, shadow copies, and system logs, while also disabling repair mechanisms and terminating critical services such as SQL and Exchange. It can even shut down Hyper-V virtual machines, further expanding its impact. Both variants share the same campaign infrastructure, including Tor-based payment portals, indicating deployment by a single affiliate. Although post-quantum cryptography is highlighted, it does not materially change the outcome for victims, as data remains inaccessible without attacker-controlled keys.
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