Learn Hacking by Actually Hacking

Difficulty

Intermediate

Vuln class

Client-Side Price Manipulation

Steps

// Objective

Intercept the checkout request for eCorp's paid plan and manipulate the price field to pay $0.01 instead of the real price.

// Tools required

BrowserDeveloper ToolsBurp Suite

// Step-by-step walkthrough

Browse the pricing page

Navigate to the eCorp Fintech pricing page. Select the Pro Plan ($99/month) and proceed to checkout. Open DevTools → Network tab before clicking "Pay".

Intercept the checkout request

Click "Pay" and catch the outgoing POST request in the Network tab. Inspect the request body.

Command / Input

POST /api/checkout Content-Type: application/json {"plan":"pro","amount":9900,"currency":"usd"}

⚑ The amount field (in cents) is being sent from the client. The server trusts whatever number arrives — it never re-derives the price from the plan name.

Resend the request with a modified price

Use DevTools "Edit and Resend" or Burp Repeater to modify the amount field to 1 (= $0.01) and resend.

Command / Input

POST /api/checkout {"plan":"pro","amount":1,"currency":"usd"}

Output

{"status":"success","message":"Payment accepted","receipt":"TXN-00291"}

⚑ The server accepted $0.01 for a $99 plan. This is the core of price manipulation — the server delegated the authoritative price to the untrusted client.

Retrieve the flag

After the successful "purchase", the flag appears on the order confirmation page.

Output

HackrGG{bus1n3ss_l0g1c_pr1c3_t4mp3r}

// Flag

Flag value

HackrGG{bus1n3ss_l0g1c_pr1c3_t4mp3r}

Shown on the order confirmation page after a successful manipulated checkout.

Plan Checkout — eCorp Fintech