Fix Business Logic Errors in Sanic
Business logic flaws in Sanic applications are logic-based vulnerabilities that automated scanners cannot detect. These occur when the application's workflow implementation fails to account for malicious state transitions, parameter tampering, or authorization bypasses. In high-performance Sanic environments, these errors typically manifest in trust-based assumptions regarding client-side data or incorrect sequencing of operations.
The Vulnerable Pattern
@app.route("/api/v1/order/refund", methods=["POST"])
async def process_refund(request):
order_id = request.json.get("order_id")
amount = request.json.get("amount")
# VULNERABLE: Trusts client-provided amount and doesn't verify ownership
order = await db.fetch_one("SELECT * FROM orders WHERE id = ?", order_id)
if order:
await payment_gateway.refund(order_id, amount)
return json({"status": "refunded"})
return json({"error": "not found"}, status=404)</code></pre>
The Secure Implementation
The vulnerable snippet suffers from two critical logic errors: IDOR (Insecure Direct Object Reference) and Parameter Tampering. It trusts the 'amount' provided by the request body instead of the database value, allowing an attacker to refund arbitrary sums. Furthermore, it lacks ownership verification, allowing any user to trigger a refund for any 'order_id'. The secure version fixes this by enforcing strict authorization (user_id check), using server-side source-of-truth for the refund amount, and implementing a state machine check to prevent race conditions or double-refund logic attacks.
@app.route("/api/v1/order/refund", methods=["POST"])
@auth_required
async def process_refund(request):
user_id = request.ctx.user.id
order_id = request.json.get("order_id")
# SECURE: Fetch original record to verify ownership and use server-side state for amount
order = await db.fetch_one(
"SELECT amount, status FROM orders WHERE id = ? AND user_id = ?",
order_id, user_id
)
if not order:
return json({"error": "Unauthorized or order not found"}, status=403)
if order['status'] == "already_refunded":
return json({"error": "Logic error: double refund attempt"}, status=400)
await payment_gateway.refund(order_id, order['amount'])
await db.execute("UPDATE orders SET status = 'already_refunded' WHERE id = ?", order_id)
return json({"status": "refunded"})</code></pre>
Your Sanic API
might be exposed to Business Logic Errors
74% of Sanic apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
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