Affected: PyPI: jupyterlab

A malicious PyPI package can place a `javascript:` URL in its `[project.urls]` metadata. JupyterLab's Extension Manager renders this as the extension's home-page link without validating the protocol, so a user who clicks the extension name executes attacker-controlled JavaScript in the JupyterLab origin.

### Details

One of the PyPI package's URL (jupyterlab/extensions/pypi.py) is copied straight into the `homepage_url` rendered by the frontend in packages/extensionmanager/src/widget.tsx#L77-L88.

```python best_guess_home_url = ( homepage_url # home_page / [project.urls] Homepage or data.get("project_url") or data.get("package_url") or documentation_url # docs_url / [project.urls] Documentation or source_url # [project.urls] Source Code or bug_tracker_url # bugtrack_url / [project.urls] Bug Tracker )

# homepage_url=best_guess_home_url ```

```tsx {entry.homepage_url ? ( <a href={entry.homepage_url} target="_blank" rel="noopener noreferrer" ...> {entry.name} </a> ) : ( <div>{entry.name}</div> )} ```

### Impact

An attacker needs to publish a package to PyPI (no access to the target). When the package appears in a victim's extension manager list and the victim clicks the extension name, the payload runs in the JupyterLab origin.

Preconditions: Extension Manager enabled with the default PyPI source, the malicious package appears in the victim's list/search results.

### Patches Patched in [4.5.9](https://github.c…