Security News Windows Notepad Vulnerability Allows Attackers to Execute Malicious Code Remotely

[Parkinsond]

Content source

https://cybersecuritynews.com/windows-notepad-rce-vulnerability/

Disclosed on February 10, 2026, Microsoft Patch Tuesday updates, the vulnerability stems from improper neutralization of special elements in commands (CWE-77: Command Injection) and carries a CVSS v3.1 base score of 8.8/10, rated “Important.”

The bug affects the modern Windows Notepad app, available via the Microsoft Store. An unauthorized attacker could exploit it over a network by tricking users into opening a booby-trapped Markdown (.md) file.

Once loaded, a malicious link inside the file prompts the app to handle unverified protocols. Clicking the link triggers Notepad to fetch and execute remote files, injecting arbitrary commands without proper sanitization.

Windows Notepad Vulnerability Allows Attackers to Execute Malicious Code Remotely

Microsoft has patched a critical remote code execution (RCE) flaw in the Windows Notepad app, tracked as CVE-2026-20841, which could let attackers run malicious code on victims' machines.

cybersecuritynews.com

 

[Sampei.Nihira]

Yes, leaving aside the fact that it affects md files, I have Notepad.exe (13 overrides) included in the Anti-Exploit software list.

 

[Parkinsond]

Yes, leaving aside the fact that it affects md files, I have Notepad.exe (13 overrides) included in the Anti-Exploit software list.

I'm using the legacy Notepad.

 

[Divergent]

Technical Analysis & Remediation

MITRE ATT&CK Mapping

T1204.002
User Execution: Malicious File (Opening the .md file).

T1204.001
User Execution: Malicious Link (Clicking the crafted link).

T1059
Command and Scripting Interpreter (Execution of the payload).

CVE Profile

ID
CVE-2026-20841.

Score
CVSS v3.1 8.8 (Important).

Weakness
CWE-77 (Command Injection) - Improper neutralization of special elements in commands.

Telemetry & Indicators

Target Artifact
Markdown (.md) files.

Trigger Mechanism
Custom URI schemes mimicking safe protocols.

Process Behavior
Notepad.exe (Store Version) spawning child processes (e.g., cmd[.]exe, powershell[.]exe) upon link interaction.

Remediation - THE ENTERPRISE TRACK (NIST SP 800-61r3)

GOVERN (GV) – Patch Management

Command
Force update of "Windows Notepad" via Microsoft Store for Business or Intune.

Validation
Ensure version is ≥ 11.2510.

DETECT (DE) – Threat Hunting

Command
Query EDR for Notepad.exe (specifically the Store app path: C:\Program Files\WindowsApps\Microsoft.WindowsNotepad...) initiating unusual network connections or spawning shells (cmd, powershell).

RESPOND (RS) – Mitigation

Command
Temporarily change the default file association for .md (Markdown) files to a code editor (e.g., VS Code) or the legacy Notepad until patching is verified.

PROTECT (PR) – Attack Surface Reduction

Command
Block or quarantine .md attachments at the Email Gateway if they originate from external sources.

Remediation - THE HOME USER TRACK (Safety Focus)

Priority 1: Update Immediately

Command
Open the Microsoft Store app → Library → Click "Get updates". Verify Notepad is updated to the latest version.

Priority 2: Behavior Check

Command
Be extremely cautious with .md files downloaded from the internet. Do not click links inside a Notepad document unless you verified the source.

Priority 3: Verification

Command
Open Notepad → Settings (Gear icon) → About. Ensure version is 11.2510 or higher.

Hardening & References

Reference

Microsoft Security Update Guide: CVE-2026-20841

Hardening & Prevention

Enable "Smart App Control" (Windows 11)

Action
Go to Windows Security → App & browser control → Smart App Control.

Why
This feature uses Microsoft's cloud intelligence to automatically block malicious or untrusted apps (like a compromised Notepad process) from running unverified scripts.

Enable "Reputation-based Protection"

Action
In the same menu (App & browser control), ensure "Check apps and files" is toggled ON.

Why
This acts as a safety net, warning you before opening unrecognized files downloaded from the web.

Attack Surface Reduction (Manual)
Windows 10/11 Pro, Enterprise, or Education.

Action
Change the default app for .md (Markdown) files. Right-click any .md file → Properties → Opens with: Change → Select VS Code or Notepad++ (if installed).

Why
This completely neutralizes the threat by bypassing the vulnerable "Store Version" of Notepad entirely.

In the enterprise, we use ASR to say, "Never let Office apps create child processes." For home users, Smart App Control effectively says, "If an app tries to do something weird that legitimate apps don't usually do, block it." It is the same logic, but packaged for consumer safety.

Source

CyberSecurityNews