Overview
Sensitive data exposure occurs when an API reveals confidential files or contents to unauthorized users. For the CVE-2026-2976 scenario, the FastApiAdmin component up to version 2.2.0 exposed file contents by directly using a client-supplied file_path in its download controller. This allowed remote attackers to request arbitrary files from the host, including configuration files, credentials, and other secrets. The vulnerability aligns with CWE-200 (Information Exposure), CWE-284 (Improper Access Control), and CWE-434 (Unrestricted Upload of File) in the sense that improper input handling and lack of access checks led to untrusted disclosure of sensitive resources.
Attack vector: An attacker supplies manipulated file_path, including directory traversal sequences, to read files outside the intended directory. The endpoint had insufficient validation and no enforcement of an allowed directory root; there was potential for remote exploitation since the exploit was publicly available.
Fix approach in real FastAPI code: The recommended fix is to stop using client-provided file_path to assemble absolute paths. Use a server-side mapping of file IDs to safe, validated paths or use a streaming approach to serve files, ensuring the resolved path stays within a designated base directory. Validate and normalize paths using pathlib, verify path.is_file(), and ensure the path startswith BASE_DIR. Always enforce authentication/authorization for download endpoints.
Notes: After upgrading to patched release, verify with tests and use security best practices; consider implementing rate limiting, authentication, and logging for sensitive endpoints; for FastAPI apps, ensure dependencies (like FastApiAdmin) are updated; incorporate CIS controls; add tests that attempt path traversal; implement content-type handling.
Affected Versions
FastApiAdmin <= 2.2.0
Code Fix Example
FastAPI API Security Remediation
Vulnerable:
from fastapi import FastAPI, HTTPException
from fastapi.responses import FileResponse
import os
app = FastAPI()
BASE_DIR = '/var/app/files'
@app.get('/download')
async def download(file_path: str):
full_path = os.path.join(BASE_DIR, file_path)
if not os.path.exists(full_path):
raise HTTPException(status_code=404, detail='Not found')
return FileResponse(full_path)
Secure (fixed):
from fastapi import FastAPI, HTTPException
from fastapi.responses import FileResponse
import pathlib
app = FastAPI()
BASE_DIR = pathlib.Path('/var/app/files').resolve()
def _resolve_safe_path(file_id: str) -> pathlib.Path:
mapping = {
'readme': BASE_DIR / 'readme.txt',
'config': BASE_DIR / 'config.ini',
}
if file_id not in mapping:
raise FileNotFoundError
resolved = mapping[file_id].resolve()
if not str(resolved).startswith(str(BASE_DIR)):
raise FileNotFoundError
return resolved
@app.get('/download')
async def download_secure(file_id: str):
try:
safe_path = _resolve_safe_path(file_id)
except FileNotFoundError:
raise HTTPException(status_code=404, detail='Not found')
if not safe_path.exists() or not safe_path.is_file():
raise HTTPException(status_code=404, detail='Not found')
return FileResponse(str(safe_path))