Business logic flaws are often overlooked by more common vulnerabilities like SQL injection and cross-site scripting (XSS). However, they can be some of the most challenging and potentially devastating types of security issues to deal with. 

In this post, we'll explore what business logic flaws are, how they're introduced, the impact they can have, and challenges in detecting and preventing them.

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What are Business Logic Flaws?

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Business logic flaws exploit the legitimate functionality of an application in ways that were not intended by the developers. Unlike many other types of vulnerabilities, business logic flaws are unique to each application because they stem from the specific business rules and workflows implemented in the software.

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Examples of Business Logic Flaws

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Let's look at some hypothetical examples to better understand how business logic flaws manifest…

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1. Discount stacking: An eCommerce site allows multiple discount codes to be applied without proper checks, enabling users to stack discounts and potentially get items for free.

2. Broken authentication flow: A password reset function emails a temporary link to the user but doesn't invalidate it after use, allowing indefinite access to the account.

3. Race conditions in banking transactions: A banking app doesn't properly handle concurrent transactions, allowing a user to withdraw more money than their balance by making simultaneous requests.

4. Insufficient authorization checks: An application allows users to access or modify data belonging to other users by manipulating request parameters.

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Where Do Business Logic Flaws Come From?

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Business logic flaws are vulnerabilities that arise from faulty application logic rather than traditional coding mistakes. They are typically introduced during the design and development phases of an application. Often as a result of incomplete or ambiguous requirements being passed to developers with insufficient consideration of edge cases or unexpected user behaviour.

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What's the Impact of Business Logic Flaws?

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The impact of business logic flaws can be severe and wide-ranging:

1. Financial losses: Flaws in pricing logic or transaction processing can lead to significant monetary damage.

2. Data breaches: Improper access controls or authorization checks can expose sensitive information.

3. Reputation damage: Public disclosure of these flaws can erode customer trust and harm brand image.

4. Regulatory non-compliance: Some logic flaws may result in violations of industry regulations or data protection laws.

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Case Study: The Spotify royalty manipulation incident

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In 2017, Spotify identified a flaw that allowed artists to artificially inflate their streaming numbers and royalty payments, impacting how they calculated and distributed royalties.

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Some artists and their teams exploited this by creating playlists with their songs, then using bots or fake accounts to stream these continuously. This falsely inflated the play counts, leading to higher royalty payments.

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The flaw existed because the system didn't adequately differentiate between genuine user engagement and automated streaming. It also didn't have proper checks in place to detect and prevent this kind of manipulation.

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This case illustrates how business logic flaws can have real-world financial implications and how they can arise from complex business models and processes that may not be immediately obvious during development.

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Challenges in Detecting and Preventing Business Logic Flaws

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Detecting and preventing business logic flaws presents unique challenges.

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Firstly, there are limitations in what automated tools can detect. Traditional SAST (Static Application Security Testing) and DAST (Dynamic Application Security Testing) tools struggle to identify business logic flaws, for example. These tools are designed to find known patterns of vulnerabilities in code or HTTP responses, but they can't understand the intended business logic of an application.

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Because automated tools fall short, identifying business logic flaws often relies on manual testing and code review. This process is time-consuming and resource-intensive, especially for large and complex applications.

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Secondly, identifying business logic flaws requires a deep understanding of the application's purpose, workflows, and business rules. This knowledge is often spread across different teams and stakeholders.

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Moreover, as business requirements change over time, new logic flaws can be introduced.

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Organisations generally rely on traditional annual or quarterly penetration tests to identify these kinds of vulnerabilities but, realistically, continuous testing and review are necessary to keep up with these changes, especially in rapidly evolving applications.

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Leveraging LLMs for Business Logic Flaw Detection

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While not a silver bullet, Large Language Models (LLMs) offer a new avenue for identifying business logic flaws. By training them to read and analyse development tickets, we can use LLMs to flag changes that have the potential to introduce business logic flaws based on patterns and context.

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What’s more, we can use generative AI to synthesise specific test cases, designed to cover each of the potential business logic flaws being introduced, covering edge cases that people often overlook.

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However, while LLMs can be a powerful tool, they are not a replacement for manual testing. They are capable of identifying the changes that warrant human intervention, and guiding testers in their efforts to identify these issues, but people are still required to actually deliver the testing itself.

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Conclusion

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The unique nature of business logic flaws represent a significant challenge in application security, making them difficult to detect through automated means, and their potential impact can be severe.

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The way to address this is through early involvement in the design phase. Strong communication between development, security, and business stakeholders, and manual testing of changes where business logic flaws might be present.

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Tools like LLMs and generative AI are a brilliant opportunity to enable this, and will only get better over time. If you’d like to understand more about how Cytix can help do exactly this for your business, book a demo and come see for yourself.