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CVE-2021-21972 — The vSphere Client (HTML5) contains a remote code execution vulnerability in a vCenter…

Key facts

CVE-2021-21972 is a Critical (9.8) vulnerability: The vSphere Client (HTML5) contains a remote code execution vulnerability in a vCenter…. This entry ships a detection-only PoC and a Docker test lab. It is on the CISA Known Exploited Vulnerabilities (KEV) catalog (added 2021-11-03), confirming active exploitation in the wild, and is linked to known ransomware campaigns.

Actively exploited — on the CISA KEV catalog

CVE-2021-21972 is listed on the CISA Known Exploited Vulnerabilities (KEV) catalog (added 2021-11-03), confirming exploitation in the wild. It is linked to known ransomware campaigns. Federal remediation deadline: 2021-11-17. Prioritise patching and deploy the detection and prevention rules below.
CVE CVE-2021-21972
Severity Critical (9.8)
CISA KEV Actively exploited (added 2021-11-03) · ransomware
Detection / prevention —
PoC poc.py
Source 2021/CVE-2021-21972/

Details

English | 한국어

Description

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).

Vulnerability Details

Property Value
CVE ID CVE-2021-21972
Type RCE
CVSS Score 9.8

Proof of Concept

Download

# Download PoC script
curl -O https://raw.githubusercontent.com/fankh/vulnerability-poc/main/2021/CVE-2021-21972/poc.py

Usage

# Run PoC against target
python3 poc.py --target <TARGET_URL>

# With authentication
python3 poc.py --target <TARGET_URL> --username <USER> --password <PASS>

⚠️ Warning: This PoC is for authorized security testing only. It uses detection-only techniques and does not exploit or damage target systems.

Test Lab

This repository includes a Docker-based test environment with both vulnerable and patched applications.

Quick Start

# Clone and navigate to CVE directory
cd CVE-2021-21972

# Start both applications
docker-compose up -d

# Run tests
./run-tests.sh    # Linux/Mac
./run-tests.ps1   # Windows PowerShell

Application Endpoints

Application URL Status
Vulnerable App http://localhost:8080 Shows vulnerability
Patched App http://localhost:8081 Demonstrates fix

Directory Structure

├── README.md           # English documentation
├── README_KO.md        # Korean documentation
├── poc.py              # PoC detection script
├── docker-compose.yml  # Container orchestration
├── run-tests.sh        # Linux/Mac test runner
├── run-tests.ps1       # Windows test runner
├── vulnerable-app/     # Vulnerable version
│   ├── app.py
│   ├── Dockerfile
│   └── requirements.txt
└── patched-app/        # Fixed version
    ├── app.py
    ├── Dockerfile
    └── requirements.txt

References

  • http://packetstormsecurity.com/files/161590/VMware-vCenter-Server-7.0-Arbitrary-File-Upload.html
  • http://packetstormsecurity.com/files/161695/VMware-vCenter-Server-File-Upload-Remote-Code-Execution.html
  • http://packetstormsecurity.com/files/163268/VMware-vCenter-6.5-6.7-7.0-Remote-Code-Execution.html
  • https://www.vmware.com/security/advisories/VMSA-2021-0002.html
  • http://packetstormsecurity.com/files/161590/VMware-vCenter-Server-7.0-Arbitrary-File-Upload.html
  • http://packetstormsecurity.com/files/161695/VMware-vCenter-Server-File-Upload-Remote-Code-Execution.html
  • http://packetstormsecurity.com/files/163268/VMware-vCenter-6.5-6.7-7.0-Remote-Code-Execution.html
  • https://www.vmware.com/security/advisories/VMSA-2021-0002.html
  • https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-21972

Generated by PoC Generator on 2026-06-26T13:06:07.346837693

Frequently asked questions

What is CVE-2021-21972?

CVE-2021-21972 is a Critical (9.8) vulnerability: The vSphere Client (HTML5) contains a remote code execution vulnerability in a vCenter…. This entry ships a detection-only PoC and a Docker test lab. It is on the CISA Known Exploited Vulnerabilities (KEV) catalog (added 2021-11-03), confirming active exploitation in the wild, and is linked to known ransomware campaigns.

How do I detect CVE-2021-21972?

Run the detection-only PoC included with this entry against your Docker test lab to confirm whether a target is affected; pair it with your own IDS logging.

How do I block or mitigate CVE-2021-21972?

Upgrade to a fixed version per the vendor advisory; the NVD record lists the affected versions. Use the included PoC to verify your remediation.

Is CVE-2021-21972 actively exploited?

Yes. CVE-2021-21972 is on the CISA Known Exploited Vulnerabilities (KEV) catalog, added 2021-11-03, which means it has been exploited in the wild. CISA also links it to known ransomware campaigns. CISA set a federal remediation deadline of 2021-11-17. Prioritise patching and deploy the detection and prevention rules above.

For authorized security testing and research only. See the full source and NVD record.