A critical implementation error in Nitrogen ransomware targeting VMware ESXi hosts effectively converts each attack into a data‑wiping event rather than a traditional extortion incident. According to technical analysis by Coveware, the flaw breaks the cryptographic relationship between the ransomware’s public and private keys, meaning that encrypted virtual machines cannot be recovered, even if the victim pays and receives a “decryptor” from the attackers.
Nitrogen ransomware on ESXi: why encrypted data cannot be decrypted
The issue affects the Nitrogen ransomware variant designed for VMware ESXi environments. In a normal ransomware operation, attackers generate a private key and derive a matching public key. Files are encrypted with the public key, and the private key held by the criminals is then used to decrypt them once a ransom is paid.
Coveware’s reverse engineering shows that Nitrogen’s ESXi encryptor instead uses a corrupted public key. As a result, no corresponding private key exists in reality. Even if the attackers act in “good faith” and provide what they believe is the correct decryption key, the math simply does not work: the key pair is broken, and encrypted data remains permanently inaccessible.
How a Curve25519 memory bug breaks Nitrogen’s key pair
Nitrogen relies on elliptic curve cryptography over Curve25519, a modern and widely used algorithm for secure key exchange. In a correct implementation, a random private key is generated first, and a mathematically linked public key is computed from it. Knowing the private key then reliably allows decryption of any data encrypted with the corresponding public key.
In the ESXi variant of Nitrogen, Coveware identified a memory handling bug on the stack. The ransomware stores the public key at stack offset rsp+0x20, but then writes a new QWORD (8‑byte) variable starting at rsp+0x1c. Because these memory regions overlap, the first four bytes of the public key are accidentally overwritten.
This means the final public key actually used for file encryption has been partially and randomly modified. It was not derived from any valid private key; it is essentially a malformed value resulting from unintended memory corruption. As Coveware notes, there is no private key that mathematically corresponds to this damaged public key, which makes decryption fundamentally impossible.
Impact on VMware ESXi environments and virtual infrastructure
The Nitrogen ESXi variant presents a particularly serious risk because it targets virtualization infrastructure rather than individual endpoints. A single compromised ESXi host can run dozens of critical virtual machines: database servers, domain controllers, file servers, backup systems, and core business applications.
When such a host is encrypted, the effect can mirror a near‑total outage of the organization’s IT environment. In typical ransomware incidents, payment decisions are often influenced by the perceived likelihood of successful data restoration. With Nitrogen’s ESXi bug, however, the ransom ceases to be a viable recovery option at all.
Organizations without recent, isolated backups face permanent data loss. This aligns with broader industry findings from multiple ransomware reports (including those by Coveware and other incident response firms) that paying a ransom never guarantees full recovery, but in this case the guarantee is mathematically zero.
Who is behind Nitrogen and where did the code come from?
The Nitrogen threat group has been active since at least 2023 and is considered a financially motivated cybercriminal operation. Researchers assess that Nitrogen likely emerged after the leak of the Conti ransomware builder into the public domain, an event that spawned multiple new ransomware families based on repurposed Conti code.
According to reporting from Barracuda Networks, Nitrogen initially operated more as a malware and initial access provider, selling tools that other threat actors could use to penetrate networks. Over time, the group pivoted to running its own full ransomware operations. By around September 2024, Nitrogen was observed directly attacking organizations and issuing ransom demands under its own brand.
Incident response and ESXi security: why paying the ransom is pointless
The cryptographic flaw in the Nitrogen ESXi encryptor has a clear operational implication: paying the ransom will not restore encrypted virtual machines. Even if attackers provide a decryptor, it cannot work against data locked with a corrupt Curve25519 public key.
Organizations that suspect a Nitrogen intrusion should immediately engage digital forensics and incident response (DFIR) specialists. Proper identification of the ransomware family, preservation of forensic evidence, and a realistic assessment of recovery options are essential. This also helps avoid wasting valuable time and money negotiating with attackers when decryption is technically impossible.
The incident underscores the critical importance of a robust backup and resilience strategy for VMware ESXi and other virtualization platforms, including:
- Maintaining offline or immutable backups that are logically and physically separated from production networks.
- Regularly testing backup restoration for ESXi hosts and key virtual machines, not just verifying that backups complete.
- Implementing strong network segmentation so that compromise of a single host does not expose the entire virtual estate.
From a preventive standpoint, organizations should strengthen ESXi security through well‑established best practices:
- Keep hypervisors, management tools, and plugins fully patched, prioritizing vulnerability remediation on internet‑exposed systems.
- Restrict direct access to ESXi management interfaces from the internet, using VPNs, jump hosts, and hardened admin workflows instead.
- Enforce least privilege and multi‑factor authentication (MFA) for all administrative accounts and remote access paths.
- Deploy EDR/XDR and centralized logging for early detection of anomalous activity affecting hypervisors and management planes.
- Conduct regular incident response exercises, explicitly including scenarios involving ESXi compromise and mass VM encryption.
The Nitrogen ransomware case illustrates that even professional cybercriminals make critical engineering mistakes, but such errors do not benefit victims. In this instance, a single flawed memory write transforms a ransomware operation into irreversible data destruction. Organizations relying on VMware ESXi and other virtual infrastructure should treat this as a warning: long before an incident occurs, invest in hardened configurations, network segmentation, disciplined backup strategies, and practiced response plans. Those preparations often make the difference between a recoverable security event and a permanent business‑critical data loss.
