But so far as I can tell the bug isn't related to "network-aware rendering stack" or AI (as other people are blindly speculating)?
From MSRC:
>How could an attacker exploit this vulnerability?
>An attacker could trick a user into clicking a malicious link inside a Markdown file opened in Notepad, causing the application to launch unverified protocols that load and execute remote files.
Sounds like a bug where you could put an url like \\evil.example\virus.exe into a link, and if a user clicks it executes virus.exe