Md2OneNote treats every Markdown file as untrusted input: the file may have come from anywhere. The add-in therefore

• never passes raw HTML through to OneNote (HTML blocks are dropped and reported, inline tags become plain text),
• embeds only images that live next to the Markdown file; absolute paths, .. traversal, network shares and remote URLs are refused,
• renders diagrams in a WebView2 with every network request blocked and no access to local files,
• bounds file size, page size, image size, diagram count and diagram time so a hostile file fails cleanly,
• makes no network connection of any kind, and has no telemetry or update check.

The full model is in docs/REQUIREMENTS.md, section 4.2.

If you find a way for a Markdown file to run code, read a file, reach the network, or damage a notebook, please do not open a public issue. Use GitHub's private vulnerability reporting on this repository (Security tab, "Report a vulnerability"). Include the Markdown that triggers it and the add-in version.

You will get an acknowledgement within a week. Fixes ship as a new release with a note in CHANGELOG.md; credit is given if you want it.

In scope: the add-in and its installer. Out of scope: OneNote itself, the WebView2 runtime, and the third-party libraries listed in THIRD-PARTY-NOTICES.md (report those upstream, and tell us so the dependency can be updated).