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Actively exploitedKnown ransomware use

CVE-2021-21972 VMware vCenter Server Remote Code Execution Vulnerability

VMware vCenter Server vSphere Client contains a remote code execution vulnerability in a vCenter Server plugin which allows an attacker with network access to port 443 to execute commands with unrestricted privileges on the underlying operating system.

From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.

Our Assessment

Should You Worry?

Patch nowCybergen assessment
  • CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 3 Nov 2021.
  • CISA lists it as known to be used in ransomware campaigns.
  • Rated Critical severity (CVSS 9.8, scored by CISA).
  • This product type is often exposed to the internet, which is where attackers scan for it first.
  • It has been in the catalogue for 1,829 days. Systems still unpatched now have almost certainly been scanned for it.
The Vulnerability

What It Is

The vSphere Client (HTML5) contains a remote code execution vulnerability in a vCenter Server plugin. 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. This affects VMware vCenter Server (7.x before 7.0 U1c, 6.7 before 6.7 U3l and 6.5 before 6.5 U3n) and VMware Cloud Foundation (4.x before 4.2 and 3.x before 3.10.1.2).

Affected Versions

ProductVersions
VMware vCenter Server7.x before 7.0 U1c
6.7 before 6.7 U3l
6.5 before 6.5 U3n
VMware Cloud Foundation4.x before 4.2
3.x before 3.10.1.2

From the public CVE record, as supplied by the vendor. Always confirm against the vendor advisory.

From Watch to Action

What To Do Now

  1. 1

    Find it

    Search your asset inventory and external attack surface for VMware vCenter Server. Include cloud images, appliances and anything a supplier runs for you.

    Attack Surface Management
  2. 2

    Fix it

    Apply updates per vendor instructions.

    Vulnerability Management
  3. 3

    Hunt for compromise

    If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.

    Incident Response
  4. 4

    Prove it is fixed

    Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.

    Penetration Testing

Vendor Advisories

Regulation

The Compliance Clock

Cyber EssentialsRated critical, so if it affects devices in your Cyber Essentials scope, the update must be installed within 14 days of the vendor releasing it.NIS2If exploitation causes a significant incident, essential and important entities owe their CSIRT an early warning within 24 hours and a notification within 72 hours.DORAFinancial entities must classify ICT incidents and send an initial notification for a major incident within strict deadlines, with exploited flaws a common cause.US federal (BOD 22-01)Federal civilian agencies had until 17 Nov 2021 to remediate. A sensible benchmark for everyone else.

General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.

Stay Ahead

More Exploited VMware Flaws

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All 26 exploited VMware vulnerabilities

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Evidence

Sources

  1. CISA Known Exploited Vulnerabilities catalogue
  2. NVD: CVE-2021-21972
  3. CVE record: CVE-2021-21972
  4. FIRST EPSS
  5. vmware.com/security/advisories/VMSA-2021-0002.html
  6. packetstormsecurity.com/files/161590/VMware-vCenter-Server-7.0-Arbitrary-File-Upload.html
  7. packetstormsecurity.com/files/161695/VMware-vCenter-Server-File-Upload-Remote-Code-Execution.html
  8. packetstormsecurity.com/files/163268/VMware-vCenter-6.5-6.7-7.0-Remote-Code-Execution.html