Fix Logic Flow Bypass in CherryPy
Logic flow bypasses in CherryPy occur when an attacker skips mandatory execution steps—like authentication checks, payment gateways, or multi-factor validation—by hitting endpoints out of order. If your application relies on client-side flags or assumes a linear request path without server-side state enforcement, you are vulnerable to state-machine manipulation and unauthorized access.
The Vulnerable Pattern
import cherrypy
class VulnerableApp:
@cherrypy.expose
def step1_register(self):
return “User details submitted.”
@cherrypy.expose
def step2_payment(self):
# Payment logic here
return "Payment confirmed."
@cherrypy.expose
def final_success(self):
# VULNERABILITY: No check to ensure step1 and step2 were completed.
# An attacker can navigate directly to /final_success.
return "Access Granted: Sensitive Data Exposed."</code></pre>
The Secure Implementation
The fix involves implementing a server-side state machine using CherryPy's session management. By assigning a specific 'flow_state' identifier to the user's session at each successful completion of a step, we can enforce a strict sequence. The 'validate_flow' helper method acts as a gatekeeper, ensuring that the 'final_success' endpoint is only reachable if the session contains the 'paid' state. This effectively prevents attackers from jumping the queue by manually crafting requests to terminal endpoints.
import cherrypy
class SecureApp:
def validate_flow(self, required_state):
if cherrypy.session.get(‘flow_state’) != required_state:
raise cherrypy.HTTPError(403, “Logic Flow Violation: Complete previous steps.”)
@cherrypy.expose
def step1_register(self):
cherrypy.session['flow_state'] = 'registered'
return "User details submitted."
@cherrypy.expose
def step2_payment(self):
self.validate_flow('registered')
# Process payment logic...
cherrypy.session['flow_state'] = 'paid'
return "Payment confirmed."
@cherrypy.expose
def final_success(self):
self.validate_flow('paid')
# Reset state after completion to prevent replay
cherrypy.session['flow_state'] = None
return "Access Granted: Secure Data Delivered."</code></pre>
Your CherryPy API
might be exposed to Logic Flow Bypass
74% of CherryPy apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
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