CVE-2026-20841: Windows Notepad App RCE Vulnerability

CVE-2026-20841 Overview

CVE-2026-20841 is a command injection vulnerability (CWE-77) affecting the Windows Notepad App. This improper neutralization of special elements used in a command allows an unauthorized attacker to execute arbitrary code locally on vulnerable systems. The vulnerability requires user interaction to exploit but does not require prior authentication.

Critical Impact

Successful exploitation enables local code execution with potential for complete compromise of confidentiality, integrity, and availability on affected Windows systems.

Affected Products

• Windows Notepad App

Discovery Timeline

• February 10, 2026 - CVE-2026-20841 published to NVD
• February 12, 2026 - Last updated in NVD database

Technical Details for CVE-2026-20841

Vulnerability Analysis

This command injection vulnerability exists due to improper neutralization of special elements within the Windows Notepad application. The flaw allows attackers to inject malicious commands that are subsequently executed in the context of the application. Exploitation requires local access and user interaction, meaning an attacker would need to convince a victim to open a specially crafted file or interact with malicious content through Notepad.

The vulnerability is classified under CWE-77 (Improper Neutralization of Special Elements used in a Command), indicating that user-controllable input is passed to a command execution context without adequate sanitization or escaping of special characters that could modify the intended command structure.

Root Cause

The root cause of this vulnerability stems from insufficient input validation and sanitization when processing certain elements within the Notepad application. Special characters or command sequences that should be treated as data are instead interpreted as executable commands, allowing injection attacks. This failure to properly neutralize special elements before they reach a command interpreter enables arbitrary code execution.

Attack Vector

The attack vector for CVE-2026-20841 is local, requiring the attacker to either have direct access to the target system or leverage social engineering to convince a user to interact with malicious content. The attack does not require any special privileges but does require user interaction. Once triggered, the injected commands execute with the privileges of the Notepad process, potentially leading to full system compromise depending on the user context.

An attacker could craft a malicious file or input that, when opened or processed by Notepad, triggers the command injection. The injected commands could then be used to download and execute additional payloads, establish persistence, exfiltrate data, or perform other malicious actions.

Detection Methods for CVE-2026-20841

Indicators of Compromise

• Unusual child processes spawned from notepad.exe, particularly command interpreters (cmd.exe, powershell.exe)
• Notepad processes making unexpected network connections or file system modifications
• Anomalous command-line arguments or encoded strings associated with Notepad execution

Detection Strategies

• Monitor process creation events for suspicious parent-child relationships involving notepad.exe
• Implement application control policies to restrict execution of scripts and commands from unexpected contexts
• Deploy endpoint detection rules to identify command injection patterns in process arguments
• Analyze file access patterns for Notepad opening files from untrusted locations

Monitoring Recommendations

• Enable enhanced process auditing (Event ID 4688) with command-line logging on Windows systems
• Configure SIEM rules to alert on notepad.exe spawning shell processes
• Implement behavioral analysis for detecting code injection techniques targeting Windows applications
• Review and monitor Windows Defender Application Control (WDAC) or AppLocker logs for policy violations

How to Mitigate CVE-2026-20841

Immediate Actions Required

• Apply the security update from Microsoft as soon as it becomes available
• Restrict user access to untrusted files and educate users about the risks of opening files from unknown sources
• Consider using alternative text editors until a patch is applied
• Implement application allowlisting to control execution of potentially malicious payloads

Patch Information

Microsoft has acknowledged this vulnerability. Refer to the Microsoft CVE-2026-20841 Advisory for official patch information and update guidance. Organizations should prioritize patching based on their Windows deployment and follow Microsoft's recommended update procedures.

Workarounds

• Avoid opening files from untrusted sources in Notepad until the patch is applied
• Use alternative text editing applications that are not affected by this vulnerability
• Implement strict email and download filtering to prevent malicious files from reaching end users
• Enable Windows Defender Exploit Guard Attack Surface Reduction (ASR) rules to mitigate code injection attacks

Organizations should monitor the Microsoft CVE-2026-20841 Advisory for additional mitigation guidance and patch availability updates.