CVE-2025-66645: Nicegui Path Traversal Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-hxp3-63hc-5366",
  "modified" : "2026-01-08T20:44:47Z",
  "published" : "2025-12-09T14:25:15Z",
  "aliases" : [ "CVE-2025-66645" ],
  "summary" : "NiceGUI has a path traversal in app.add_media_files() allows arbitrary file read",
  "details" : "### Summary\n\nA directory traversal vulnerability in NiceGUI's `App.add_media_files()` allows a remote attacker to read arbitrary files on the server filesystem.\n\n### Details\n\nHello, I am Seungbin Yang, a university student studying cybersecurity. \nWhile reviewing the source code of the repository, I discovered a potential vulnerability and successfully verified it with a PoC.\n\nThe `App.add_media_files(url_path, local_directory)` method allows users to serve media files. However, the implementation lacks proper path validation.\n\n```python\ndef add_media_files(self, url_path: str, local_directory: Union[str, Path]) -> None:\n    @self.get(url_path.rstrip('/') + '/{filename:path}')\n    def read_item(request: Request, filename: str, nicegui_chunk_size: int = 8192) -> Response:\n        filepath = Path(local_directory) / filename\n        if not filepath.is_file():\n            raise HTTPException(status_code=404, detail='Not Found')\n        return get_range_response(filepath, request, chunk_size=nicegui_chunk_size)\n```\nRoot Cause:\n1. The `{filename:path}` parameter accepts full paths, including traversal sequences like `../`.\n2. The code simply joins local_directory and filename without checking if the result is still inside the local_directory.\n3. There is no path sanitization or boundary check.\n\nConsequence:\nAn attacker can use `..` to access files outside the intended directory. If the application has permission, sensitive files (e.g., /etc/hosts, source code, config files) can be exposed.\n\n### POC\n1. Create `poc.py`:\n```python\n# poc.py\nfrom pathlib import Path\nfrom nicegui import app, ui\n\nMEDIA_DIR = Path(__file__).parent / 'media'\nMEDIA_DIR.mkdir(exist_ok=True)\n\n# Expose local \"media\" directory at /media\napp.add_media_files('/media', MEDIA_DIR)\n\n@ui.page('/')\ndef index():\n    ui.label('NiceGUI media PoC')\n\nui.run(port=8080, reload=False)\n```\n\n2. Run the application: `python3 poc.py`\n\n3. Exploit with curl: Use URL-encoded dots (`%2e`) to bypass client-side checks.\n```curl -v \"http://localhost:8080/media/%2e%2e/%2e%2e/%2e%2e/etc/hosts\"```\n\n\n### Result:\nThe HTTP status is 200 OK, and the response body contains the contents of the server’s /etc/hosts file.\n\nI have attached a screenshot of the successful exploitation below. As shown in the image, the content of /etc/hosts displayed via cat matches the output received from the curl request perfectly.\n\n<img width=\"1728\" height=\"1078\" alt=\"POC screenshot\" src=\"https://github.com/user-attachments/assets/6c1be75b-6be2-4372-90df-55042c1e4775\" />\n\n### Impact\n\nAny NiceGUI application that calls app.add_media_files() on a URL path reachable by an attacker is affected. An unauthenticated remote attacker can read sensitive files outside the intended media directory, potentially exposing:\n\n•Application source code and configuration files\n•Credentials, API keys, and secrets\n•Operating system configuration files (e.g., /etc/passwd, /etc/hosts)\n\nThis is my first github vulnerability report, so I would appreciate your understanding regarding any potential shortcomings. If you require any further information or clarification, please feel free to contact me at y4rvin@naver.com.\n\nThank you.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "nicegui"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.4.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/zauberzeug/nicegui/security/advisories/GHSA-hxp3-63hc-5366"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2025-66645"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/zauberzeug/nicegui/commit/a1b89e2a24e1911a40389ace2153a37f4eea92a9"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/zauberzeug/nicegui"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-12-09T14:25:15Z",
    "nvd_published_at" : "2025-12-09T22:16:15Z"
  }
}