Business Logic Vulnerabilities: Examples and 4 Best Practices

Oliver Moradov

What Are Business Logic Vulnerabilities?

Business logic vulnerabilities are design and implementation flaws in software applications. They have a legitimate business function, but can also be exploited by malicious attackers to create unexpected behavior. These flaws often result from an application’s inability to identify and safely handle unexpected user actions.

In most applications, business logic is implemented with defined rules, constraints, and user workflows. These rules and flows are defined either at the design stage or easier, when defining business requirements. Developers build these constraints into applications, defining how the application will behave. However, a weak point is the implementation of appropriate access rights at each point of the user flow. Depending on how user inputs are handled and parameters passed to functions and APIs, business logic vulnerabilities can occur.

Business logic flaws are often difficult to detect and vulnerability management can be challenging. Typically, identifying them requires cooperation between individuals who deeply understand the business and manual testing teams. 

Automated testing of business logic vulnerabilities is challenging, but a new generation of tools can achieve it using artificial intelligence (AI) and fuzz testing technology. An example of such a tool is Bright Security DAST.

In this article:

Adding Business Logic Vulnerabilities to the Vulnerability Management Process

The risks associated with flaws in business logic are context-specific and depend on the nature of the business. Organizations must perform threat modeling, leveraging knowledge of the business processes carried out by the application, to accurately identify threat agents. 

Another aspect of vulnerability assessment is to identify processes related to revenue streams. These processes, if interrupted, could cause major damage to the organization. They could also be attractive for attackers to target because of their financial value.

Business logic flaws are very common in large application projects involving large development teams. Developers who work on specific modules or components may not fully understand the work done by other developers, and might make incorrect assumptions. Without proper coordination and documentation, these assumptions can become vulnerabilities that can impact application security.

Organizations need a process for regularly checking existing applications and new code for business logic vulnerabilities. This should be a part of the overall vulnerability management strategy. When the organization tests for and remediates known vulnerabilities in its applications, it must not neglect business logic vulnerabilities.

Business Logic Vulnerability Examples

Excessive Trust in Client-Side Controls

A fundamentally flawed assumption is that the user only interacts with the application through the provided web interface. This is especially dangerous because it leads to the additional assumption that client-side validation prevents the user from providing malicious input. 

However, attackers can use proxy tools to tamper with data after it is sent from the browser and before it is passed to server-side logic. This effectively disables client-side controls.

Accepting data at face value without performing proper integrity checks and server-side validation allows an attacker to do major damage with minimal effort. What they can achieve depends on the application’s capabilities and the value of the data it holds.

Making Flawed Assumptions About User Behavior

One of the most common root causes of business logic bugs is wrong assumptions about user behavior. Commonly, developers don’t consider potentially dangerous scenarios that violate these assumptions. 

For example, applications can appear secure because they implement a robust way to enforce business rules. However, some developers don’t realize that users and data within the application cannot be trusted indefinitely after passing these strict controls. By applying constraints only at the beginning of the interaction, and failing to verify them later, these applications can allow privilege escalation. 

In general, if business rules and security measures are not applied consistently across applications and throughout user interactions, they can create potentially dangerous vulnerabilities that attackers can exploit.

Domain-Specific Flaws

Many logical flaws are related to the specific business domain or the subject matter of a specific application. An example is a discount feature in an eCommerce website. This is a significant attack surface, because it allows attackers to explore underlying logical flaws in the way discounts are applied.

In general, any application function that makes it possible to adjust prices, make payments, or modify any sensitive data value based on user interaction, must be carefully considered. It is important to understand the algorithms the application uses to make these adjustments and in which circumstances they occur. A good way to test this is to manipulate these types of functions, attempting user inputs that will lead to unexpected results.

4 Critical Best Practices for Business Logic Vulnerability Management

Identifying business logic vulnerabilities requires determining how an application should work and understanding how attackers might exploit the business logic. Penetration testers use this information to design and test threat scenarios. Human creativity allows attackers (and pentesters) to find workarounds.

Identifying Logic Flaws

Security analysts should assess the codebase to understand the business rules and logic of the application. They should identify the security controls in place, how they work, and any control gaps. 

Understanding the Software

To protect the software, security, testing, and development teams must understand it fully. Organizations should compile lists of known vulnerabilities, licenses, and code components. Scanning the codebase can help identify vulnerabilities.

Automating Security Processes

Vulnerability management processes are often too complex and time-consuming for human security and dev teams to handle alone. Organizations should utilize automated testing tools like Interactive Application Security Testing (IAST), Static Application Security Testing (SAST), and Dynamic Application Security Testing (DAST).

Prioritizing Vulnerabilities

Security teams should use the insights from scans and analysis tools to prioritize high-risk vulnerabilities. It is often impractical to address all vulnerabilities quickly, so prioritization allows developers to fix the most pressing issues first. 

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