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Broken Function Level Auth I

rest-api-security | Level: Easy  | Total Lab Runs: 0 | Premium Lab

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Lab Walkthrough Video:

Securing an API is a critical task. A poor API design may lead to system compromise. Its impact becomes more critical when a crucial service gets affected like a Banking API.

The Banking WebApp provides its customers, the ability to view their balances and the bank employees have read and write access to the user accounts. The authorization system relies on a scope parameter present in the token issued to any authenticated user. If the token issued to a user has the scope of "account", then they get read-write access on the account. The Banking API provides a Golden Ticket when the balance of a user exceeds $5000000.

This challenge is focused on leveraging the Broken Function Level Authorization in the Banking API.

Objective: Leverage the vulnerability to increase your account balance and retrieve the Golden Ticket from the Bank API!

User Information:


API Endpoints:

Issue a JWT Token used as an authorization mechanism
identifier, password
Read the balance of an account
acct, token
Modify the account balance
POSTacct, token, balance
Get the Golden Ticket from the Bank API


  • This lab is dedicated to you! No other users are on this network :)
  • Once you start the lab, you will have access to a Kali GUI instance.
  • Your Kali instance has an interface with IP address 192.X.Y.2. Run "ifconfig" to know the values of X and Y.
  • The Banking WebApp is running on port 5000 on the target machine having IP address 192.X.Y.3.
  • Do not attack the gateway located at IP address 192.X.Y.1

1. Golden Ticket

The following activities are strictly prohibited on this website unless otherwise explicitly stated as allowed in the mission statement:

  • Using automated scanners
  • Using brute force attacks
  • Denial of Service attacks
  • Attacking other student machines in challenges where you might achieve a shell on the vulnerable system
  • Attacking the lab infrastructure

Users violating the above will be either temporarily or permanently banned from the website. 

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Technical Support for this Lab:

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