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Race Condition

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

Lab Scoreboard

Lab Walkthrough Video:

On the occasion of their 10th anniversary, Secure E-Wallet Ltd. has a new issued a new redeem code "RX100" which is one time and would increase user balance (by at max $100).

The redeem implementation works as follows:

  1. It maintains a redeem count set to 1.
  2. Once the token is redeemed the redeem count is reduced by 1, that is, redeem = redeem - 1
  3. If the redeem count is 0, the redeem code cannot be used further.

Note: To avoid API abuse, the developers have placed a rate limit on all of the API Endpoint. The API allows only 10 requests per second.

Once the account balance exceeds $5000, the user gets a Golden Ticket.

The issue is that the redeem operation is a bit slow and the developers hadn't placed any checks to avoid any race conditions.

Objective: Leverage this fault to increase the balance and get the Golden Ticket.

User Information:


  • 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 Secure E-Wallet application should be running on port 5000 on the machine located at the 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. 

If you are unsure about an activity, then please contact support to confirm that it is allowed on our website.

Technical Support for this Lab:

There is a reason we provide unlimited lab time: you can take as much time as you need to solve a lab. However, we realize that sometimes hints might be necessary to keep you motivated!

We currently provide technical support limited to:

  • Giving hints for a lab exercise
  • In rare circumstances, if you have totally given up (NO!!!) then tell you how to solve it. This will be limited to sharing the solution video or lab report
  • A lab exercise fails to load or has errors in it

If you need technical support, please email  clearly mention the name and link of the lab exercise and other essential details. The more descriptive you are, the faster we can help you. We will get back to you within 24 hours or less. 

For adminitrative queries, billing, enterprise accounts etc. please email