Fix Logic Flow Bypass in TurboGears
Logic flow bypass in TurboGears typically occurs when controller methods trust client-provided parameters to dictate state transitions or authorization levels. Attackers manipulate the request to skip validation steps or escalate privileges by injecting parameters that the application logic fails to verify against the server-side session or identity state.
The Vulnerable Pattern
from tg import expose, request
class RootController(BaseController): @expose() def process_payment(self, order_id, amount, validated=False): # VULNERABILITY: The ‘validated’ flag is accepted directly from the request. # An attacker can call /process_payment?order_id=123&amount=0.01&validated=True # to bypass the internal business logic validation steps. order = Order.query.get(order_id) if validated: order.status = ‘paid’ order.amount = amount return ‘Order Processed’ return ‘Validation Failed’
The Secure Implementation
The vulnerable code suffers from a parameter injection flaw where a sensitive boolean flag ('validated') is exposed to the user. Attackers can override this flag in the query string or POST body to bypass logic checks. The secure implementation removes the flag from the method signature, enforces authorization using the '@require' decorator with 'tg.predicates', and validates the order state against the authenticated user's session and internal database state.
from tg import expose, request, predicates, require
class RootController(BaseController):
@expose()
@require(predicates.has_permission(‘execute_payment’))
def process_payment(self, order_id, amount):
# FIX: Remove client-controlled flags. Use server-side session identity
# and strict state machine transitions.
order = Order.query.filter_by(id=order_id, user_id=request.identity[‘user’].id).one()
if not self._internal_verify_order(order, amount):
return 'Validation Failed'
order.status = 'paid'
return 'Order Processed'
def _internal_verify_order(self, order, amount):
# Private method for server-side integrity check
return order.amount == amount and order.status == 'pending'</code></pre>
Your TurboGears API
might be exposed to Logic Flow Bypass
74% of TurboGears apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
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