Fix BOLA (Broken Object Level Authorization) in Hug

BOLA (OWASP API1:2023) is the bread and butter of API exploitation. In the Hug framework, it manifests when you expose an internal object ID (like a UUID or integer) in a route and fail to verify if the authenticated requester actually owns that specific resource. If you're just querying by ID and returning the result, you're leaking data.

The Vulnerable Pattern

import hug
@hug.get(‘/api/v1/invoice/{invoice_id}’)
def get_invoice(invoice_id):
# CRITICAL VULNERABILITY: No ownership check.
# An attacker can iterate ‘invoice_id’ to scrape the entire DB.
return db.fetch_invoice(invoice_id)

The Secure Implementation

To kill BOLA in Hug, you must move beyond simple authentication. Use Hug's 'context' to pass the authenticated user object. When querying your persistence layer, always include the user's unique identifier (e.g., owner_id) in the WHERE clause. If the record doesn't exist for that specific user, return a 404 'Not Found' rather than a 403 'Forbidden' to prevent attackers from discovering which IDs are valid.

import hug
from marshmallow import fields
@hug.get(‘/api/v1/invoice/{invoice_id}’)
def get_invoice(invoice_id, context):
user = context.get(‘user’)
if not user:
return hug.output.not_found()
# SECURE: Scope the query to the user's account
invoice = db.session.query(Invoice).filter_by(
    id=invoice_id, 
    owner_id=user.id
).first()

if not invoice:
    # Return 404 to prevent resource enumeration
    return hug.output.not_found()

return invoice</code></pre>