Shadow APIs in Hug manifest when developers expose internal functions via decorators without enforcing versioning, authentication, or documentation controls. This creates an unmanaged attack surface where legacy or debug endpoints remain live, invisible to security scanners but reachable by attackers fuzzing the router. To kill shadow APIs, you must enforce explicit versioning and implement global authentication requirements.

The Vulnerable Pattern

import hug
Vulnerable: No versioning, no authentication, and no type validation.
This endpoint is ‘shadowed’—it exists in production but isn’t tracked or secured.
@hug.get(‘/debug_user_info’)
def get_user_info(user_id):
return {‘user_id’: user_id, ‘internal_status’: ‘active’, ‘role’: ‘admin’}
@hug.get(‘/api/data’)
def legacy_data():
return {‘data’: ‘old_format_sensitive_info’}

The Secure Implementation

The fix involves three pillars: 1. Versioning: Using @hug.version(n) ensures that all endpoints are part of a tracked lifecycle, preventing 'floating' legacy routes. 2. Explicit Type Validation: Using hug.types prevents parameter injection and unexpected behavior during fuzzing. 3. Global/Route Authentication: Using the 'requires' argument ensures that even if an endpoint is discovered, it cannot be abused without valid credentials. Finally, setting include_in_documentation=False for non-public utility routes prevents them from appearing in automatically generated API docs while maintaining visibility for the dev team.

import hug
from marshmallow import fields
Secure: Enforce versioning, strict type validation, and authentication.
authentication = hug.authentication.api_key(lambda key: key == ‘secure_token’)
@hug.version(1)
@hug.get(‘/user_info’, requires=authentication)
def get_user_info_v1(user_id: hug.types.number):
"""Official V1 User Info Endpoint"""
return {‘user_id’: user_id}
Explicitly disable or hide internal routes if they must exist
@hug.get(‘/health’, include_in_documentation=False)
def health_check():
return {‘status’: ‘ok’}