How I Earned $500 in One Day by Discovering a Business Logic Vulnerability in a Forex Web Application

Introduction

During a security assessment, I identified a business logic vulnerability in a forex trading web application.
The issue stemmed from insufficient validation and authorization checks, which enabled me to:

• Transfer funds from another user’s account.
• Withdraw funds using an account that did not own the balance.

For responsibly reporting this vulnerability, I received a $500 reward within one day.
This case demonstrates how improper validation of user actions can lead to severe financial and reputational risks for organizations in the fintech industry.

• Vulnerability Details
  • Impact
  • Root Cause
• Recommendations
• Conclusion

Vulnerability Details

The application failed to properly enforce ownership validation when performing critical actions such as fund transfers and withdrawals. By manipulating requests at the business logic layer, I was able to execute transactions on behalf of other accounts without authorization.

Impact

• Unauthorized fund movement between accounts.
• Potential for large-scale financial fraud.
• Loss of trust in the platform’s integrity.

Root Cause

The application relied solely on client-side or insufficient server-side checks to verify whether the requesting account truly owned the funds being transferred or withdrawn.

Recommendations

To mitigate this vulnerability, the following actions are recommended:

1. Enforce strict server-side validation to ensure that only the rightful account owner can initiate transfers and withdrawals.
2. Implement robust authorization controls at every sensitive function.
3. Add audit logging and anomaly detection for unusual transaction behavior.
4. Conduct regular security assessments focusing on business logic flaws.

Conclusion

This case highlights how business logic vulnerabilities, though less technical than traditional exploits, can have serious real-world consequences, especially in the financial sector.
By addressing validation gaps and strengthening authorization controls, organizations can significantly reduce their exposure to these high-impact risks.

As a security researcher, this finding not only improved the platform’s security posture but also rewarded me with $500 in just one day — a clear reminder of the value of responsible disclosure.