Fix BOLA (Broken Object Level Authorization) in Sanic
BOLA (OWASP API1:2023) is the ultimate low-hanging fruit for API exploitation. It occurs when a Sanic handler blindly trusts a user-supplied ID from the URI or body without verifying the requester's ownership of that specific resource. If an attacker can iterate through IDs and dump data that isn't theirs, your authorization logic is broken. We fix this by enforcing strict ownership checks at the data access layer or via decorators.
The Vulnerable Pattern
from sanic import Sanic, responseapp = Sanic(“BOLA_Vulnerable”)
VULNERABLE: Any authenticated user can access any user_id profile
@app.get(“/api/v1/user/<user_id:int>/settings”) async def get_settings(request, user_id): # The app assumes that because the user is logged in, # they are allowed to see whatever ID they put in the URL. settings = await db.fetch_row(“SELECT * FROM settings WHERE user_id = ?”, user_id) return response.json(settings)
The Secure Implementation
To kill BOLA in Sanic, stop trusting the path parameters. The fix involves implementing an authorization layer that compares the identity in the session/JWT (request.ctx) against the ID of the object being requested. In the secure example, a decorator acts as a gatekeeper. If the 'user_id' in the URL doesn't match the 'id' of the authenticated requester, the request is terminated with a 403 Forbidden before the database is even queried. For complex objects (like a post ID), you must query the database to verify that the 'owner_id' of that post matches the 'request.ctx.user.id' before returning the data.
from sanic import Sanic, response, exceptions from functools import wrapsapp = Sanic(“BOLA_Fixed”)
def check_ownership(): def decorator(f): @wraps(f) async def decorated_function(request, *args, **kwargs): # 1. Extract the authenticated user (e.g., from a JWT middleware) current_user_id = request.ctx.user.get(‘id’) requested_resource_id = kwargs.get(‘user_id’)
# 2. Explicitly validate ownership if str(current_user_id) != str(requested_resource_id): raise exceptions.Forbidden("Unauthorized: You do not own this resource.") return await f(request, *args, **kwargs) return decorated_function return decorator
@app.get(“/api/v1/user/<user_id:int>/settings”) @check_ownership() async def get_settings(request, user_id): settings = await db.fetch_row(“SELECT * FROM settings WHERE user_id = ?”, user_id) return response.json(settings)
Your Sanic API
might be exposed to BOLA (Broken Object Level Authorization)
74% of Sanic apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
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