Fix Logic Flow Bypass in Helidon

Logic flow bypasses in Helidon SE/MP apps occur when developers assume a linear execution path based on UI navigation. Attackers skip 'boring' steps (like payment or MFA) and hit the final 'success' endpoints directly. If your handlers don't enforce a strict Finite State Machine (FSM) validation on the server-side, you're leaking business logic. Stop trusting the client's position in the flow.

The Vulnerable Pattern

routing.post("/api/checkout/finalize", (req, res) -> {
    // VULNERABILITY: No check to see if step1 (shipping) and step2 (payment) were actually completed.
    // Attacker can POST here directly to trigger order fulfillment.
    var orderId = req.queryParams().first("id").get();
    orderService.ship(orderId);
    res.send("Order shipped successfully");
});

The Secure Implementation

The fix requires implementing a server-side state tracker. In Helidon, use the request Context or a distributed cache (like Redis) to store the user's progress. Every sensitive handler must verify that the prerequisite state has been achieved. Never rely on the client to tell you what step they are on; verify the session's 'State' token or database record before executing terminal logic. For stateless microservices, use a signed JWT 'Flow-Token' that is updated and re-issued after each successful step.

routing.post("/api/checkout/finalize", (req, res) -> {
    var orderId = req.queryParams().first("id").get();
    var session = req.context().get(UserSession.class).orElseThrow();
// SECURE: Validate state transition server-side
if (session.getCurrentState(orderId) != OrderState.PAYMENT_VERIFIED) {
    res.status(403).send("Logic bypass detected: Payment not verified for this order.");
    return;
}

orderService.ship(orderId);
session.updateState(orderId, OrderState.SHIPPED);
res.send("Order shipped successfully");
});