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The VMware ESXi ransomware attacks reported in February 2023 were known as ESXiArgs. CISA and the FBI said attackers may have exploited known vulnerabilities in unpatched, outdated, or out-of-service ESXi servers—but VMware did not confirm which CVE or CVEs were used. The incident was not established as a new zero-day attack, and the official sources do not give a current count of affected systems.
What happened in the ESXiArgs attack?
CISA and the FBI issued a joint advisory on February 8, 2023, describing ransomware activity against VMware ESXi servers. They said open-source reporting indicated that attackers were exploiting known vulnerabilities and likely targeting unpatched or end-of-life systems. VMware likewise said reports pointed to outdated or unsupported products and stated on February 6, 2023: “VMware has not found evidence that suggests an unknown vulnerability (0-day) is being used to propagate the ransomware used in these recent attacks.”
The scale figure is historical: the February 8, 2023 CISA/FBI advisory reported that ESXiArgs actors had compromised over 3,800 servers globally. That is not a present-day estimate. The official materials cited here do not establish how many systems remain vulnerable or compromised.
Which vulnerability did the attackers exploit?
VMware’s Q&A, updated February 16, 2023, said the CVEs involved were unknown at that time. It noted that media reports had speculated about CVE-2021-21974, but VMware had no evidence that this was the only attack vector. It would therefore be inaccurate to present that CVE as the confirmed, sole cause of the campaign.
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The sources support a narrower conclusion: the campaign was associated with known vulnerabilities and vulnerable or unsupported ESXi systems, but the exact exploit path was not established in VMware’s published Q&A. Applying updates and reducing management-interface exposure were core elements of official guidance.
What did ESXiArgs do to virtual machines?
CISA and the FBI said ESXiArgs encrypted certain virtual-machine configuration files, potentially leaving VMs unusable. In the cases described in their advisory, virtual-machine flat files were not encrypted. That left open the possibility of reconstructing some configuration files and restoring access to affected VMs; it did not mean every system could be recovered.
What should administrators do to prevent a similar incident?
Keep ESXi supported and updated
CISA and the FBI advised updating ESXi to the latest version. VMware recommended using supported releases and applying updates promptly. Because support status and patch builds change, administrators should check VMware’s current advisories and product lifecycle information for the specific version in use rather than relying on 2023 version references.
Reduce exposure and harden management access
- Do not expose the ESXi hypervisor to the public internet. CISA and the FBI’s February 8, 2023 advisory put it plainly: “Ensure the ESXi hypervisor is not exposed to the public internet.”
- Disable the Service Location Protocol (SLP) service where appropriate, as CISA and the FBI recommended. VMware’s Q&A cautioned that disabling SLP/CIM may affect third-party monitoring or management functions in some environments, so assess dependencies first.
- Restrict access to infrastructure management interfaces, use multifactor authentication, and apply vSphere hardening guidance, as VMware recommended.
VMware’s February 6, 2023 post said ESXi 7.0 U2c and newer, and ESXi 8.0 GA and newer, shipped with OpenSLP disabled by default. Those are historical product details, not a current version or patch recommendation; verify present-day support and configuration with VMware before acting.
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Prepare for recovery before an incident
- Maintain offline backups and regularly test both backup integrity and restoration.
- Protect backup data from alteration, including through immutability, and ensure backups cover the organization’s data infrastructure.
- Maintain and exercise an incident response plan.
What should you do if you suspect an ESXiArgs infection?
- Isolate affected hosts. CISA and the FBI advised quarantining or taking affected hosts offline to reduce the risk of reinfection.
- Bring in incident response expertise. VMware advised consulting an incident response team before taking recovery steps. Preserve relevant information and have responders assess the host, environment, and available backups.
- Review recovery options before running tools. CISA and the FBI published a script intended to automate reconstruction of certain configuration files. They advised reviewing it for suitability and understanding its effects before deployment; it is an attempt, not a guaranteed recovery method, and the script is provided without warranty.
- Restore carefully and validate service. Assess backup quality and the state of the environment with responders before bringing hosts or VMs back online. The official sources do not provide a recovery success rate or a universal procedure that fits every deployment.
Prevention or recovery: which path applies?
| Situation | Priority | Practical focus |
|---|---|---|
| No suspected compromise | Preventive maintenance | Use supported, updated software; restrict management access and public exposure; assess SLP dependencies; and maintain tested, protected backups. |
| Compromise suspected or confirmed | Incident response and recovery | Isolate affected hosts, involve incident responders, assess backups and environment state, and consider the CISA script only after reviewing its suitability and effects. |
There is no single step that substitutes for both paths. The right response depends on whether compromise is suspected, the host’s support status, operational requirements, service dependencies, backup readiness, and an environment-specific assessment.
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Official sources
- VMware Security Response Center: Response to “ESXiArgs” Ransomware Attacks, February 6, 2023.
- VMware: ESXiArgs Questions & Answers, updated February 16, 2023.
- CISA and FBI: ESXiArgs Ransomware Virtual Machine Recovery Guidance, February 8, 2023.
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