Affected: jupyterlab-git

JupyterLab Git is a Git extension for JupyterLab. Prior to 0.54.0, jupyterlab-git uses fnmatch.fnmatchcase() in GitHandler.prepare() in jupyterlab_git/handlers.py to enforce excluded_paths, allowing an authenticated user on a case-insensitive filesystem to vary URL path casing and read excluded directories. This issue is fixed in version 0.54.0.

Affected: PyPI: jupyterlab-git

## Summary

`jupyterlab-git` 0.53.0 (latest, 2026-04-30) uses `fnmatch.fnmatchcase()` in `GitHandler.prepare()` (`jupyterlab_git/handlers.py:91`) to enforce the admin-configured `excluded_paths` security control. Because `fnmatchcase` is unconditionally case-sensitive, an authenticated user on a case-insensitive filesystem (macOS APFS, Windows NTFS) can bypass the exclusion by varying the case of the URL path segment — e.g. requesting `/git/project/Secrets/...` instead of `/git/project/secrets/...` — gaining read access to git history, file content, and status in directories the administrator explicitly excluded.

## Vulnerable Code

```python # jupyterlab_git/handlers.py:84-92 async def prepare(self): """Check if the path should be skipped""" await ensure_async(super().prepare()) path = self.path_kwargs.get("path") if path is not None: excluded_paths = self.git.excluded_paths for excluded_path in excluded_paths: if fnmatch.fnmatchcase(path, excluded_path): # ← always case-sensitive raise tornado.web.HTTPError(404) ```

## Root Cause

`fnmatch.fnmatchcase()` is unconditionally case-sensitive regardless of the operating system. Contrast with `fnmatch.fnmatch()` which normalizes via `os.path.normcase()` on case-insensitive platforms.

```python fnmatch.fnmatchcase("/project/secrets", "/project/secrets") # True — blocked fnmatch.fnmatchcase("/project/Secrets", "/project/secrets") # False — bypasses check ```

On ma…