Overview
CVE-2026-2977 documents a real-world Broken Object Level Authorization (BOLA) flaw in FastApiAdmin up to version 2.2.0, where the Scheduled Task API's upload_controller allowed unrestricted file uploads. This ties to CWE-284 (Improper Access Control) and CWE-434 (Unrestricted Upload of File). An attacker could remotely exploit the endpoint by manipulating a resource_id and uploading arbitrary content without checking ownership or permissions, potentially leading to remote code execution, storage of malicious files, or abuse of shared storage. The public disclosure of the exploit underscores the high risk in multi-tenant deployments where multiple users share a single upload location. In FastAPI-based apps, this kind of misstep typically arises when an API trusts the client-side identifiers for access decisions and bypasses server-side ownership verification. The vulnerability exposes the need for robust object-level authorization checks in FastAPI handlers that act on user-owned resources and upload assets tied to those resources.
In practice, exploitation occurs when an endpoint accepts a resource_id path parameter and a file to upload but does not verify that the current authenticated user owns the resource or has rights to modify it. Because the authorization decision is effectively based on a parameter supplied by the client, an attacker can target other users' resources by supplying their IDs in the request, enabling unrestricted uploads to those resources. The CVE notes indicate public disclosure and active exploitation opportunities, which heightens the urgency for developers to enforce strict server-side access controls and to harden upload handling in FastAPI services.
To remediate in a real FastAPI codebase, implement explicit object-level authorization checks using the authenticated user context, and avoid relying solely on client-provided identifiers for access decisions. Enforce ownership verification before performing any resource-modifying actions, restrict upload content types and sizes, canonicalize and sanitize filenames, and store uploads in per-resource or per-user locations with strict filesystem boundaries. Consider adopting a centralized authorization policy (RBAC or ABAC), integrating with OAuth2/JWT dependencies for current_user, and adding automated tests that simulate BOLA scenarios. After applying the fix, validate with end-to-end tests that attempt cross-user uploads and ensure those are rejected with 403 Forbidden regardless of the request parameters.
Affected Versions
FastApiAdmin <= 2.2.0 (CVE-2026-2977)
Code Fix Example
FastAPI API Security Remediation
from fastapi import FastAPI, Depends, UploadFile, File, HTTPException
from pydantic import BaseModel
import os
app = FastAPI()
UPLOAD_ROOT = "uploads"
class User(BaseModel):
id: int
# Mock DB to illustrate ownership
DB = {
1: {"owner_id": 1, "name": "Resource 1"},
2: {"owner_id": 2, "name": "Resource 2"},
}
def get_current_user():
# In a real app, extract user from JWT/OIDC; here we simulate an authenticated user with id 1
return User(id=1)
# Vulnerable pattern: uses resource_id but does not verify ownership
@app.post("/resources/{resource_id}/upload-vuln")
async def upload_vuln(resource_id: int, file: UploadFile = File(...), current_user: User = Depends(get_current_user)):
resource = DB.get(resource_id)
if resource is None:
raise HTTPException(404, "Resource not found")
dest = os.path.join(UPLOAD_ROOT, str(resource_id), file.filename)
os.makedirs(os.path.dirname(dest), exist_ok=True)
with open(dest, "wb") as f:
content = await file.read()
f.write(content)
return {"status": "uploaded", "path": dest}
# Fixed pattern: enforce ownership and allow-list file types
@app.post("/resources/{resource_id}/upload-fixed")
async def upload_fixed(resource_id: int, file: UploadFile = File(...), current_user: User = Depends(get_current_user)):
resource = DB.get(resource_id)
if resource is None:
raise HTTPException(404, "Resource not found")
if resource["owner_id"] != current_user.id:
raise HTTPException(403, "Forbidden")
allowed_types = {"image/png", "image/jpeg", "application/pdf"}
if file.content_type not in allowed_types:
raise HTTPException(400, "Unsupported file type")
dest = os.path.join(UPLOAD_ROOT, str(resource_id), file.filename)
os.makedirs(os.path.dirname(dest), exist_ok=True)
with open(dest, "wb") as f:
content = await file.read()
f.write(content)
return {"status": "uploaded", "path": dest}