Fix Logic Flow Bypass in Hug
Logic flow bypass in Hug APIs occurs when developers fail to enforce state transitions between multi-step endpoints. Attackers skip 'gatekeeper' routes (like authentication or payment confirmation) and jump directly to 'action' routes. If the action handler trusts the client-side state or assumes previous steps were completed without server-side verification, the security model is compromised.
The Vulnerable Pattern
import hugStep 1: User initiates reset
@hug.post(‘/request-reset’) def request_reset(email): # Logic to send email return {‘message’: ‘Check your email’}
Step 2: VULNERABLE - No verification that Step 1 occurred
@hug.post(‘/complete-reset’) def complete_reset(user_id, new_password): # CRITICAL: Attacker can call this directly with any user_id # bypassing the email verification link entirely. db.update_user_password(user_id, new_password) return {‘status’: ‘success’}
The Secure Implementation
The vulnerability lies in the stateless nature of the '/complete-reset' endpoint which accepts a raw 'user_id'. To fix this, we implement a signed token mechanism. The secure version uses 'itsdangerous' to generate a cryptographically signed token in the first step. The final endpoint requires this token, ensuring the user actually followed the intended logic flow. By verifying the token server-side, we prevent attackers from jumping straight to the password update logic without authorization.
import hug
from itsdangerous import URLSafeTimedSerializer
SECRET_KEY = ‘hacker-proof-secret’
s = URLSafeTimedSerializer(SECRET_KEY)
@hug.post(‘/request-reset’)
def request_reset(email):
token = s.dumps(email, salt=‘password-reset’)
# Send token via email…
return {‘status’: ‘token_generated’}
@hug.post(‘/complete-reset’)
def complete_reset(token, new_password):
try:
# SECURE: Validate that the process was initiated and the token is valid
email = s.loads(token, salt=‘password-reset’, max_age=3600)
except:
return hug.HTTP_401
db.update_user_password_by_email(email, new_password)
return {'status': 'password_updated'}</code></pre>
Your Hug API
might be exposed to Logic Flow Bypass
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