Summary: Microsoft has patched a critical security flaw in the Windows 11 Notepad app (CVE-2026-20841). The vulnerability allowed attackers to execute remote code by tricking users into clicking malicious Markdown links. By leveraging unverified protocols, the app could launch remote files without displaying standard Windows security warnings.
Business Impact: High risk for technical staff. Since Notepad is the default tool for many admins and developers, a single “one-click” exploit in a `.md` file could lead to full workstation compromise. This highlights that even “simple” text editors are now complex attack surfaces.
Why It Happened: The recent addition of Markdown support to Notepad introduced “clickable link” functionality that failed to sanitize non-standard URI schemes (like `ms-appinstaller://`), allowing them to bypass shell security checks.
Recommended Executive Action: Ensure Windows 11 systems are updated via the Microsoft Store to Notepad version 11.2601 or higher. Advise developers to treat `.md` files from external sources with the same caution as `.exe` files.
Hashtags: #Notepad #Microsoft #RCE #CommandInjection #PatchTuesday #AppSec