Fix Logic Flow Bypass in Sanic
Logic flow bypasses in Sanic occur when application state transitions are trust-based rather than strictly enforced. Attackers often 'jump' directly to sensitive endpoints (like /admin/update or /checkout/finalize) by bypassing the intermediate validation steps. In Sanic, this usually manifests as missing session-state checks or improper middleware scoping.
The Vulnerable Pattern
from sanic import Sanic, responseapp = Sanic(“VulnerableApp”)
@app.post(“/step-1-payment”) async def payment(request): # Process payment… request.ctx.session[“paid”] = True return response.json({“status”: “success”})
@app.post(“/step-2-ship”) async def ship(request): # VULNERABILITY: This endpoint assumes step-1 was completed # but never verifies the session state. item_id = request.json.get(“item_id”) return response.json({“shipping”: “initiated”, “item”: item_id})
The Secure Implementation
The fix implements a server-side state machine. Instead of trusting the client's request sequence, we use a custom decorator to validate a 'flow_state' variable stored in the encrypted session. If the user attempts to hit the shipping endpoint without the 'payment_confirmed' flag, the request is dropped. Additionally, clearing the state after the final step prevents 'State Replay' attacks where an attacker re-uses a successful state to trigger multiple actions.
from sanic import Sanic, response, exceptions from functools import wrapsapp = Sanic(“SecureApp”)
def enforce_step(required_state): def decorator(f): @wraps(f) async def decorated_function(request, *args, **kwargs): if request.ctx.session.get(“flow_state”) != required_state: raise exceptions.Forbidden(“Illegal flow transition detected.”) return await f(request, *args, **kwargs) return decorated_function return decorator
@app.post(“/step-1-payment”) async def payment(request): # Process payment logic… request.ctx.session[“flow_state”] = “payment_confirmed” return response.json({“status”: “success”})
@app.post(“/step-2-ship”) @enforce_step(“payment_confirmed”) async def ship(request): # State is verified via decorator before execution item_id = request.json.get(“item_id”) # Reset state after completion to prevent replay request.ctx.session[“flow_state”] = None return response.json({“shipping”: “initiated”})
Your Sanic API
might be exposed to Logic Flow Bypass
74% of Sanic apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
Free Tier • No Credit Card • Instant Report
Verified by Ghost Labs Security Team
This content is continuously validated by our automated security engine and reviewed by our research team. Ghost Labs analyzes over 500+ vulnerability patterns across 40+ frameworks to provide up-to-date remediation strategies.