BFLA in Hug occurs when sensitive functions are exposed without verifying the caller's specific privilege level. In many cases, developers assume standard authentication is enough, allowing any registered user to hit administrative endpoints. To fix this, we implement granular authorization checks using Hug's 'requires' parameter to enforce Role-Based Access Control (RBAC) at the function level.

The Vulnerable Pattern

import hug
VULNERABLE: No function-level authorization
Any authenticated user can delete any other user
@hug.delete(‘/api/v1/users/{user_id}’)
def delete_user(user_id: hug.types.text):
# Business logic to delete user from DB
return {‘status’: ‘success’, ‘deleted’: user_id}

The Secure Implementation

The vulnerable snippet lacks authorization logic, meaning the 'delete_user' function is accessible to anyone who can reach the route. The secure implementation uses the 'requires' argument in the Hug decorator. This acts as a gatekeeper, executing a predicate function (is_admin) before the endpoint logic. If the predicate returns False, the request is rejected. This enforces the principle of least privilege by ensuring that only users with the 'ADMIN' claim can invoke sensitive state-changing operations.

import hug
from falcon import HTTP_403
def is_admin(request, **kwargs):
"""Predicate to verify user has admin role"""
# In a real scenario, decode JWT or check session store
user_role = request.headers.get(‘X-USER-ROLE’)
if user_role == ‘ADMIN’:
return True
return False
@hug.delete(‘/api/v1/users/{user_id}’, requires=is_admin)
def delete_user(user_id: hug.types.text):
"""SECURE: Only users passing the is_admin check can execute this"""
return {‘status’: ‘success’, ‘deleted’: user_id}
@hug.exception(Exception)
def handle_exception(exception, response):
response.status = HTTP_403
return {‘error’: ‘Insufficient permissions’}