Full Report
Because of this bug, the corrupted public key is used in the key exchange to encrypt each file. Normally, when a public-private Curve25519 keypair is generated, the private key is generated, first and then the public key derived subsequently based on the private key. The resulting corrupted public key wasn't generated based on a private key, it was generated by mistakenly overwriting a few bytes of another public key. The final outcome is that no one actually knows the private key that goes with the corrupted public key. Files that were encrypted with the corrupted public key can not be decrypted by any means, including by paying a ransomware. The threat actor themselves will be unable to decrypt the files in a test. Organizations impacted by Nitrogent Ransomware encryption must be extremely careful when analyzing their recovery options. Any ESXi encrypted files that are without viable backups, must be analyzed in conjunction with the corresponding malware that encrypted them to ascertain their status.
Analysis Summary
# Vulnerability: Nitrogen Ransomware ESXi File Encryption Corruption Bug
## CVE Details
- CVE ID: N/A (This is a ransomware flaw, not a traditional vendor vulnerability)
- CVSS Score: N/A
- CWE: N/A
## Affected Systems
- Products: ESXi Servers (Targeted by Nitrogen Ransomware variant)
- Versions: Not specified; any environment targeted by the specific version of Nitrogen ESXi malware exhibiting this bug.
- Configurations: Environments where ESXi hosts were encrypted by the buggy Nitrogen ransomware.
## Vulnerability Description
The Nitrogen ESXi ransomware contains a critical coding error during the encryption process for each file. During key exchange setup, the malware incorrectly handles memory adjacent to where the file-specific Curve25519 public key is stored on the stack (at offset `rsp+0x20`). Specifically, a QWORD variable (8 bytes starting at `rsp+0x1c` through `rsp+0x24`) is written, causing **4 bytes of the public key to be overwritten with zeros (0x00s)**.
Because the public key is corrupted mid-generation, it is no longer mathematically derivable from any corresponding private key. This results in **irrevocably encrypted files**, as neither the victim nor the threat actor can determine the correct private key necessary for decryption.
## Exploitation
- Status: This is a **self-inflicted flaw** by the threat actor (Nitrogen Ransomware malware misuse) leading to irreversible data loss for victims who pay. Data is effectively unrecoverable even if the threat actor attempts to assist.
- Complexity: N/A (Not an external exploit against a product)
- Attack Vector: Execution of the ransomware payload against ESXi systems.
## Impact
- Confidentiality: High (Files are encrypted)
- Integrity: High (Files are permanently rendered unusable/modified)
- Availability: Critical (Files cannot be recovered via conventional means, including paying the ransom.)
## Remediation
### Patches
- **None applicable.** This is a flaw in the ransomware payload itself, not in a vendor product like VMware ESXi. The "patch" is utilizing backups prior to infection.
### Workarounds
- **Analyze the Malware:** Victims without viable backups must analyze the specific version of the Nitrogen malware that encrypted their files in conjunction with the encrypted data to ascertain the exact status of file corruption.
- **Do Not Pay:** Paying the ransom will not help, as the attacker cannot decrypt the files due to the key corruption.
## Detection
- **Indicators of Compromise:** Files exhibiting signs of encryption by Nitrogen (extension changes or specific file footer modification, although the file corruption itself is the primary IOC).
- **Detection Methods and Tools:** Standard ransomware detection mechanisms applied to the ESXi host filesystem monitoring or behavioral analysis of executed processes matching known Nitrogen indicators.
## References
- Vendor advisories: N/A (Vendor is Coveware, providing analysis)
- Relevant links: [Coveware Article on Nitrogen Ransomware Bug](https://www.coveware.com/blog/2026/2/2/nitrogen-ransomware-esxi-has-a-bug)