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CVE-2021-20038 — A Stack-based buffer overflow vulnerability in SMA100 Apache httpd server's mod_cgi…

Key facts

CVE-2021-20038 is a Critical (9.8) vulnerability: A Stack-based buffer overflow vulnerability in SMA100 Apache httpd server's mod_cgi…. This entry ships a detection-only PoC and a Docker test lab. It is on the CISA Known Exploited Vulnerabilities (KEV) catalog (added 2022-01-28), confirming active exploitation in the wild, and is linked to known ransomware campaigns.

Actively exploited — on the CISA KEV catalog

CVE-2021-20038 is listed on the CISA Known Exploited Vulnerabilities (KEV) catalog (added 2022-01-28), confirming exploitation in the wild. It is linked to known ransomware campaigns. Federal remediation deadline: 2022-02-11. Prioritise patching and deploy the detection and prevention rules below.
CVE CVE-2021-20038
Severity Critical (9.8)
CISA KEV Actively exploited (added 2022-01-28) · ransomware
Detection / prevention —
PoC poc.py
Source 2021/CVE-2021-20038/

Details

English | 한국어

Description

A Stack-based buffer overflow vulnerability in SMA100 Apache httpd server's mod_cgi module environment variables allows a remote unauthenticated attacker to potentially execute code as a 'nobody' user in the appliance. This vulnerability affected SMA 200, 210, 400, 410 and 500v appliances firmware 10.2.0.8-37sv, 10.2.1.1-19sv, 10.2.1.2-24sv and earlier versions.

Vulnerability Details

Property Value
CVE ID CVE-2021-20038
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-2021-20038/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-2021-20038

# 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

  • https://github.com/jbaines-r7/badblood
  • https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0026
  • https://www.rapid7.com/blog/post/2022/01/11/cve-2021-20038-42-sonicwall-sma-100-multiple-vulnerabilities-fixed-2/
  • https://github.com/jbaines-r7/badblood
  • https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0026
  • https://www.rapid7.com/blog/post/2022/01/11/cve-2021-20038-42-sonicwall-sma-100-multiple-vulnerabilities-fixed-2/
  • https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-20038

Generated by PoC Generator on 2026-06-26T01:22:51.271630312

Frequently asked questions

What is CVE-2021-20038?

CVE-2021-20038 is a Critical (9.8) vulnerability: A Stack-based buffer overflow vulnerability in SMA100 Apache httpd server's mod_cgi…. This entry ships a detection-only PoC and a Docker test lab. It is on the CISA Known Exploited Vulnerabilities (KEV) catalog (added 2022-01-28), confirming active exploitation in the wild, and is linked to known ransomware campaigns.

How do I detect CVE-2021-20038?

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-2021-20038?

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-2021-20038 actively exploited?

Yes. CVE-2021-20038 is on the CISA Known Exploited Vulnerabilities (KEV) catalog, added 2022-01-28, which means it has been exploited in the wild. CISA also links it to known ransomware campaigns. CISA set a federal remediation deadline of 2022-02-11. Prioritise patching and deploy the detection and prevention rules above.

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