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Fencer Vulns
critical 9.8

CVE-2021-21985 kev+ ransomware in the critical feed json

The vSphere Client (HTML5) contains a remote code execution vulnerability due to lack of input validation in the Virtual SAN Health Check p…

published 2021-05-26 5 y ago modified 2026-08-12 2 mo ago also EUVD-2021-9156

cvss
9.8
version 3.1, CNA
cisa kev
Exploited
added 2021-11-03, used in ransomware
epss
100.0%
EPSS 100.0% chance of exploitation in 30 days, percentile 99.9%
public exploits
1
Metasploit, plus a Nuclei check

Summary

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.

Patch / fix

cisa required action Apply updates per vendor instructions.

  • vmware cloud_foundation 3.10.2.1, 4.2.1

Timeline

  1. First public exploit (Metasploit exploit/linux/http/vmware_vcenter_vsan_health_rce)
  2. CISA SSVC: exploitation active
  3. Published
  4. Added to CISA KEV
  5. CISA patch deadline

Known exploited

Added
5 y ago
Patch by
2021-11-17 (4 y ago)
Ransomware
Known to be used in ransomware campaigns
Required action
Apply updates per vendor instructions.
Vendor, product
VMware, vCenter Server
CISA name
VMware vCenter Server Improper Input Validation Vulnerability

Ransomware

Groups reported to have exploited it in intrusions.

  • Conti ransomware gang

reported by tenable.com

Ransomware Vulnerability Matrix by BushidoUK (github.com/BushidoUK/Ransomware-Vulnerability-Matrix), reformatted per CVE. CC BY 4.0

CISA SSVC

Exploitation
Active, exploited in the wild
Automatable
yes
Technical impact
total
Assessed
5 y ago

Exploit prediction

100.00% chance of exploitation in the next 30 days, higher than 99.9% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

CVSS scores

assigned by version score vector
CISA ADP 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CNA 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 10.0 AV:N/AC:L/Au:N/C:C/I:C/A:C

Affected products

  • n/a VMware vCenter Server and VMware Cloud Foundation

Classification

Weakness
  • CWE-20 Improper Input Validation
  • CWE-470 Use of Externally-Controlled Input to Select Classes or Code
  • CWE-918 Server-Side Request Forgery
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.