The vulnerability depends on user interaction by opening a malicious notebook with Markdown cells, or Markdown file using JupyterLab preview feature.

A malicious user can access any data that the attacked user has access to as well as perform arbitrary requests acting as the attacked user.

JupyterLab v4.0.11 was patched.

Users can either disable the table of contents extension by running:

jupyter labextension disable @jupyterlab/toc-extension:registry

Vulnerability reported via the bug bounty program [sponsored by the European Commission](https://commission.europa.eu/news/european-commissions-open-source-programme-office-starts-bug-bounties-2022-01-19 en) and hosted on the Intigriti platform.