Vulnerable code sample

import os
import argparse
import uvicorn
from starlette.applications import Starlette
from starlette.responses import FileResponse, Response
from starlette.routing import Route
from starlette.requests import Request

# This handler represents the vulnerable code from src/pipecat/runner/run.py
async def download_file(request: Request):
    # The base folder is taken from the command-line arguments.
    base_folder = request.app.state.folder
    # The filename is taken directly from the URL path.
    filename = request.path_params['filename']

    # VULNERABILITY: The untrusted 'filename' is directly joined with the
    # base folder path without any sanitization or containment checks.
    # An attacker can use URL-encoded path traversal sequences like '..%2F'
    # to access files outside the intended 'base_folder' directory.
    file_path = os.path.join(base_folder, filename)

    if os.path.isfile(file_path):
        return FileResponse(file_path)
    return Response("File not found", status_code=404)

# This block simulates the runner's setup process.
if __name__ == "__main__":
    parser = argparse.ArgumentParser()
    # The '--folder' flag is required to expose the vulnerable endpoint.
    parser.add_argument("--folder", default=".", help="Path to the folder to serve files from")
    args = parser.parse_args()

    app = Starlette(routes=[
        Route("/files/{filename:path}", download_file, methods=["GET"]),
    ])
    # The folder path is stored in the application state, accessible by the handler.
    app.state.folder = os.path.abspath(args.folder)

    uvicorn.run(app, host="0.0.0.0", port=8000)