A business logic vulnerability is a defect in an application’s design and implementation that gives attackers the ability to make it behave unintentionally. As such, threat actors can manipulate legitimate functionality to achieve malicious goals.

A business logic vulnerability generally occurs when program developers fail to anticipate unusual application states. As such, the application doesn’t have a built-in failsafe, allowing them to either crash or get compromised.

Other interesting terms…

Read More about a “Business Logic Vulnerability”

Before diving into the nitty-gritty of a business logic vulnerability, let’s define what “business logic” is first.

What Is Business Logic?

In the context of a business logic vulnerability, “business logic” is the set of rules that define how a specific program operates. Despite using the term “business,” the rules aren’t always directly related to a business. As such, a business logic vulnerability is also known as an “application logic vulnerability” or a “logic flaw.”

Can Normal Users Spot Business Logic Vulnerabilities?

Normal application users can’t often see a business logic vulnerability. But attackers can because they make it a point to interact with the program in ways its developers never intended or anticipated.

Think of it this way: You expect e-commerce app users to follow a predetermined process for every transaction. The purchase process for credit card transactions could have these steps:

Add product to cart → Choose credit card payment option → Undergo credit card verification → Choose shipping option → Pay for purchase → Get transaction receipt

A business logic vulnerability occurs when hackers, for instance, skip the card verification process and go straight to payment by exploiting an app flaw. In such a case, they can use a stolen or fake credit card and not get flagged until it’s time for the company to obtain the payment from the supposed credit card provider or bank.

Why Does a Business Logic Vulnerability Occur?

While business logic vulnerabilities can differ from one application to another, they can occur because of the following scenarios:

  • Trusting client-side controls too much: Developers should never assume users will only interact with applications through their web interfaces. Hackers will do everything to get under the hood of a target program. They can change how their copy of the target program behaves, allowing them to manipulate transactions.
  • Failing to address unconventional inputs: Developers need to determine all possible scenarios and build ways to handle them into an application. They need to tell the program what inputs to accept and how it should react. So, if they forget to program a reaction to a specific scenario, the application can behave unexpectedly, which attackers can take advantage of.
  • Giving users a window into encrypted content: Developers can also make so-called “encryption oracles” available to users. An encryption oracle is the ciphertext (encrypted) version of user-controllable inputs. If threat actors use ciphertext to encrypt data using the correct algorithm and asymmetric key, they can manipulate the program.

How Do You Avoid a Business Logic Vulnerability?

You can avoid a business logic vulnerability by keeping these best practices in mind:

  • Developers must avoid making implicit assumptions about user behaviors or even how the application behaves. Don’t build in assumptions that don’t have straightforward solutions.
  • Developers should document all the assumptions they made and verify their logic.
  • Developers should ensure that all input values are sensible.
  • Developers and testers should fully understand all assumptions and how the application should react to the identified scenarios.
  • Developers should write code as clearly as possible. If the code is hard to understand, it will be challenging to spot logic flaws.
  • If developers use other code (from other applications), they should consider all the side effects of program dependencies because if hackers manipulate these, their programs can get compromised.

What Attacks Usually Employ a Business Logic Vulnerability?

Attackers can use a business logic vulnerability to:

  • Bypass authentication and escalate privileges: All applications have a list of authorized users, but if threat actors find a way to insert themselves into that access list, they can make the program do whatever they want.
  • Bypass business flows: We described this scenario earlier with the payment process example. It happens when attackers find a way to skip a step in a process by manipulating a program’s code, allowing them to control how an app behaves.
  • Exploiting client-side business routines embedded in JavaScript, Flash, or Silverlight: Many websites use these applications on forms and other interactive objects. All of the bugs in these applications can affect sites and programs that use them.

As you’ve seen, a business logic vulnerability is not a one-time mistake caused by human error. It is often the result of bad coding practices. All programs have weaknesses that can make business processes fail. You can address such flaws as early as possible in the development process by testing and continuous improvement.