CVE-2020-6819 — Under certain conditions, when running the nsDocShell destructor, a race condition can…¶

Q: How do I detect CVE-2020-6819?

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.

Q: How do I block or mitigate CVE-2020-6819?

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

Q: Is CVE-2020-6819 actively exploited?

Yes. CVE-2020-6819 is on the CISA Known Exploited Vulnerabilities (KEV) catalog, added 2021-11-03, which means it has been exploited in the wild. CISA set a federal remediation deadline of 2022-05-03. Prioritise patching and deploy the detection and prevention rules above.

Key facts

CVE-2020-6819 is a High (8.1) vulnerability: Under certain conditions, when running the nsDocShell destructor, a race condition can…. 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.

Actively exploited — on the CISA KEV catalog

CVE-2020-6819 is listed on the CISA Known Exploited Vulnerabilities (KEV) catalog (added 2021-11-03), confirming exploitation in the wild. Federal remediation deadline: 2022-05-03. Prioritise patching and deploy the detection and prevention rules below.


CVE	CVE-2020-6819
Severity	High (8.1)
CISA KEV	Actively exploited (added 2021-11-03)
Detection / prevention	—
PoC	poc.py
Source	2020/CVE-2020-6819/

Details¶

English | 한국어

Description¶

Under certain conditions, when running the nsDocShell destructor, a race condition can cause a use-after-free. We are aware of targeted attacks in the wild abusing this flaw. This vulnerability affects Thunderbird < 68.7.0, Firefox < 74.0.1, and Firefox ESR < 68.6.1.

Vulnerability Details¶

Property	Value
CVE ID	CVE-2020-6819
CVSS Score	8.1

Proof of Concept¶

Download¶

# Download PoC script
curl -O https://raw.githubusercontent.com/fankh/vulnerability-poc/main/2020/CVE-2020-6819/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-2020-6819

# 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://bugzilla.mozilla.org/show_bug.cgi?id=1620818
https://usn.ubuntu.com/4335-1/
https://www.mozilla.org/security/advisories/mfsa2020-11/
https://www.mozilla.org/security/advisories/mfsa2020-14/
https://bugzilla.mozilla.org/show_bug.cgi?id=1620818
https://usn.ubuntu.com/4335-1/
https://www.mozilla.org/security/advisories/mfsa2020-11/
https://www.mozilla.org/security/advisories/mfsa2020-14/
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2020-6819

Generated by PoC Generator on 2026-07-30T21:23:53.122122403

Frequently asked questions¶

What is CVE-2020-6819?¶

CVE-2020-6819 is a High (8.1) vulnerability: Under certain conditions, when running the nsDocShell destructor, a race condition can…. 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.

How do I detect CVE-2020-6819?¶

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-2020-6819?¶

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-2020-6819 actively exploited?¶

Yes. CVE-2020-6819 is on the CISA Known Exploited Vulnerabilities (KEV) catalog, added 2021-11-03, which means it has been exploited in the wild. CISA set a federal remediation deadline of 2022-05-03. Prioritise patching and deploy the detection and prevention rules above.

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