Managing business logic vulnerabilities

Dirk Schrader at Netwrix explains how attackers weaponise your application’s own logic against you

 

Organisations are well-versed in defending against known exploits, such as those catalogued as CVEs, and are increasingly prepared for zero-day vulnerabilities. However, there is another category of risk that often gets overlooked: business logic vulnerabilities.

 

A business logic vulnerability is a flaw in the design or implementation of an application’s core processes that makes it possible for someone to exploit the legitimate processing flows of the application to achieve an unintended outcome. This can leave organisations exposed to risks that traditional security measures may not detect.

 

 

Types of business logic vulnerabilities

While business logic vulnerabilities can stem from coding errors, they more commonly result from misunderstanding of the application’s operational rules, insufficient validation or incorrect assumptions about user behaviour. 

 

The discount loop

In most cases, a single exploitation of a business logic vulnerability causes far less damage than a traditional data breach. However, repeated incidents can result in death by a thousand cuts. 

 

For example, suppose a retailer distributes codes for discounts to kick off the spring buying season. Although these coupons are intended for one-time use, a logic flaw in the system fails to invalidate them after use — enabling each customer to reuse the same code repeatedly for weeks. This type of vulnerability nearly cost payment processor Stripe dearly; fortunately, an ethical hacker reported exactly how they were able to repeatedly redeem a “one-time” $20,000 fee discount code. 

 

Lack of input validation 

Failing to validate input can open the door for attackers to tamper with data. For example, a customer who inputs a negative quantity of an item might generate a refund in their shopping cart. 

 

Lack of user context validation

This flaw can enable improper access to sensitive data. For instance, suppose that patients access their records through a URL like this: clinic.com/records?patientID=101. If requests are not properly validated, a user could improperly access the records of other patients simply by changing the number in the “patientID” parameter. 

 

This type of vulnerability was exploited in 2024 when third-party contractors were able to abuse their access to the Quantas airline booking site and redirect the frequent flyer points of hundreds of customers into an account they controlled. 

 

 

Finding vulnerabilities

Many types of security vulnerabilities can be uncovered using conventional detection strategies. However, business logic flaws can be notoriously difficult to find — they won’t appear in a security feed or be catalogued under known CVEs. 

 

Indeed, these issues often slip past automated code reviews because the underlying code is functioning as intended; instead, it is the underlying logic that is flawed. Automated pen testing, even when it is powered by AI, often fails to detect business logic vulnerabilities for exactly the same reason. 

 

 

Defending against vulnerabilities

Defending against cybersecurity threats usually requires a multi-layered strategy that spans prevention, detection and response. Here are some key best practices to implement.

 

Educate development teams

Developers need comprehensive training in defensive coding practices such as strict input validation and error handling.  They must understand how to document an application’s intended business rules and implement context-aware authorisation checks and process flow validation as appropriate. 

 

Have human pen-testers look for flaws

While automation can play a part in preventing business logic vulnerabilities, this is an area in which the human penetration testers are indispensable because of their creativity, intuition and adversarial mindset. While developers often assume that users will follow predefined paths, testers can challenge these assumptions. They can examine the way in which an application is supposed to work and then identify deviations that create unintended consequences. 

 

In short, human pen testers start with the question “What if I misuse this feature in a way the developers never anticipated?” and work through as many scenarios as they can devise. The results can reveal where developers need to add safeguards like input validation and reauthentication.

 

Enforce strong access control 

Rigorously enforcing the principle of least privilege using a role-based access control (RBAC) approach is a core best practice that helps protect sensitive data from unauthorised access. Much as you map the proper flow of the application, you can map data access patterns to user roles and flag excessive permissions, like those that enabled the third-party contractors at Qantas to manipulate customers’ frequent-flier records. 

 

Monitor for suspicious activity

Continuous monitoring is vital for detecting potential business logic attacks in real time and responding promptly and effectively. By correlating identified anomalies with user context and historical activity, security teams can more accurately distinguish between legitimate use and malicious exploitation.

 

 

Building comprehensive security

While abuse of business logic vulnerabilities may not be an existential threat to your business, mitigating them is an important part of any comprehensive cybersecurity strategy.

 

By understanding the common types of business logic flaws and following core best practices, you can help ensure that the legitimate operations of your applications cannot be manipulated to produce unintended outcomes that could cause real damage.

 

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Dirk Schrader is VP of Security Research and Field CISO EMEA at Netwrix

 

Main image courtesy of iStockPhoto.com and guvendemir