How a Business Logic Vulnerability Led to Unlimited Discount Redemption

It sounds straightforward enough, but business logic vulnerabilities can result in an array of serious security issues, such as unauthorized access, bypassing rate limits, or in the case of a recent Stripe vulnerability, unlimited redemption of considerable discounts. The true impact of business logic vulnerabilities depends on the functionality being exploited.

What Is a Business Logic Vulnerability?

Business logic flaws stem from design and coding mistakes in how input data is processed, failure to validate assumptions, gaps in handling edge cases, race conditions, and other coding errors that lead to violations of the intended business rules and security policies. In essence, these vulnerabilities enable attackers to manipulate an application's legitimate but flawed logic to their advantage.

These vulnerabilities allow an attacker to circumvent or abuse legitimate application functionality in unintended ways to achieve a malicious goal, such as:

• Gaining unauthorized access to data/functionality
• Modifying application data in violation of constraints
• Conducting unauthorized transactions or operations
• Bypassing rate limits, quotas, or other restrictions
• Escalating privileges inappropriately

Business logic vulnerabilities are different from traditional “technical” vulnerabilities, such as improper access control and information disclosure. Some more technical organizations may have a good grasp on addressing the more common vulnerabilities, requiring hackers to have a more creative mindset to exploit features through errors in business logic. Hackers who may not be as technically adept but bring a creative approach to security research may be more attracted to testing for business logic vulnerabilities.

What Is the Business Impact of Business Logic Vulnerabilities?

The business impact of a business logic vulnerability can be significant, as it can potentially lead to financial losses, data breaches, and damage to an organization's reputation and customer trust. 

1. Financial Loss: Attackers may be able to conduct fraudulent transactions, unauthorized purchases, or gain access to financial accounts/data.
2. Data Breaches: Business logic flaws can allow unauthorized access to sensitive data, such as personal information, financial records, or intellectual property. 
3. Reputational Damage: A publicized data breach or exploitation of a logic flaw can severely damage an organization's reputation and credibility.
4. Competitive Disadvantage: Intellectual property or trade secrets could be compromised, providing competitors with an unfair advantage.
5. Operational Disruptions: Attackers may be able to disrupt business operations, e.g., by depleting resources or overwhelming systems through exploitation of logic flaws.
6. Non-Compliance Penalties: Depending on the nature of the vulnerability, it may result in non-compliance with industry regulations or standards, especially in the financial services industry, leading to penalties or loss of certifications.

What Industries Are Impacted By Business Logic Errors?

According to the 8th Annual Hacker-Powered Security Report, business logic errors are within the top 10 most common vulnerabilities, at 2% of all vulnerabilities reported via the HackerOne platform. While 2% may not seem like much, it's a 5% year-over-year increase from 2023, meaning business logic errors are becoming more common. 

While business logic error does not discriminate by industry, it is more prominent in some industries than others. Two percent of vulnerabilities in the financial services industry are business logic errors, aligning with the frequency of the vulnerability across the board. 

However, Cryptocurrency and Blockchain organizations experience a much higher rate of 10%. Cryptocurrency and Blockchain is a progressive tech industry that is more experienced at solving the most commonly found vulnerabilities, such as cross-site scripting. Therefore, security researchers need to be more creative by identifying different ways features can be exploited and testing business logic vulnerabilities. The industry places a lot of value in these bugs, putting 45% of their total bounty awards toward business logic errors.

Take a look at how many of your vulnerabilities are business logic errors compared to the average for your industry.

An Example of a Business Logic Error Vulnerability Found on Stripe

HackerOne’s Hacktivity resource showcases disclosed vulnerabilities on the HackerOne Platform. Check it out to see how specific weaknesses have been identified and fixed. The following business logic error example demonstrates how a hacker discovered a vulnerability in Stripe that could allow unlimited fee discounts.

Customer: Stripe
Vulnerability: Business logic error
Severity: Medium

Summary

Hacker @ian discovered a business logic vulnerability where fee discounts on Stripe could be redeemed multiple times, resulting in unlimited fee-free transactions. While somewhat unconventional, the hacker is a real Stripe customer and used his real Stripe account to test the discovery.

Impact

Ian was offered a fee discount of $20,000 on Stripe transactions. Stripe Support applied the offer to his account, and he was shown a prompt to accept the fee discount in his dashboard. Ian used the Turbo Intruder extension within Burp Suite to make rapid requests in parallel to accept the discount. He called the endpoint 30 times, and each time, the discount was applied successfully to his account, resulting in $600,000 of fee-free transactions. The hacker concluded this would cost Stripe about 3% of each discount, or $600 each time a $20,000 discount is abused.

Remediation

Initially, Stripe attempted to fix the issue by adding a check, but Ian demonstrated there was still a race condition allowing multiple redemptions. After another iteration by Stripe's team, Ian confirmed the vulnerability was fully resolved and could no longer be exploited.

While Stripe was able to fully resolve the issue, the potential for significant financial losses, legal exposure, and reputational damage highlights the criticality of identifying and fixing business logic vulnerabilities, especially in financial platforms. 

Reward

The hacker received a $5,000 bounty and gratitude from the Stripe team for helping them avoid an incident. 

Secure Your Organization From Business Logic Vulnerabilities With HackerOne

This is only one example of the pervasiveness and impact severity of business logic vulnerabilities. HackerOne and the community of ethical hackers are best equipped to help organizations identify and remediate these and other vulnerabilities, whether through bug bounty, Pentest as a Service (PTaaS), Code Security Audit, or other solutions by considering the attacker's mindset on discovering a vulnerability.

Download the 8th Annual Hacker-Powered Security Report to learn more about the impact of the top 10 HackerOne vulnerabilities, or contact HackerOne to get started taking on bugs at your organization.