You may think it requires writing hundreds of lines of code to break through the most secure network defenses. In reality, cybercriminals typically gain access to your sensitive data through the standard functionalities of your API, used in a way you didn't anticipate. 

These loopholes are called Business Logic Flaws, and they are your biggest threat to your API security.

What Are Business Logic Flaws?

A business logic vulnerability is a flaw in an API's design that lets an attacker manipulate legitimate functionalities, data, or workflows to reach a malicious goal.

Business logic flaws are so prevalent that four of the top five OWASP API attack vectors are related to this cluster of vulnerabilities, making it vital for you to understand how they work.

From elevating user privileges to destroying databases, the key factor is that these flaws occur due to incorrect assumptions about how different parts of your systems work and interact.

As a real-world example, a business logic vulnerability was the root cause of a massive data breach involving the United States Postal Service and 60 million records of sensitive user data, leaving a permanent mark on the organization's reputation.

Read More: What is API Security and Why It's Important

How Do Business Logic Flaws Happen?

APIs are the pipelines that are allowed through the firewall. And if they're not tested properly, they could be vulnerable - essentially, by design - with business logic flaws.

Corey Ball, Cybersecurity Consulting Manager & Author of "Hacking APIs"

When an attacker tries to access your network systems using malware, SQL injections, or other techniques, even the most basic security measures will likely trigger an alarm and warn your security teams about an ongoing cyberattack.

With business logic flaws, it's an entirely different story.

Imagine a scenario where your dev team overlooks restriction protocols that allow HTTP request methods on the page displaying the current balance of a user's bank account. The attacker could potentially use the PUT method to edit the value or delete the record entirely.

Since logic flaws like this happen within the bounds of legitimate API functionalities, they typically don't trigger any alarms until long after your data has been compromised - if ever.

Businesses suffer financial losses, decreased customer confidence, damaged reputations, and even bankruptcy due to data breaches.

Read More: What is API Testing Automation?

What Are the Most Common Types of Business Logic Flaws?

While business logic flaws are unique vulnerabilities based on the architecture of a given API, we can single out the most common types of them to help you stay ahead of cybercriminals.

1. Misusing HTML Elements and Other Client-side Code

Web pages are often built using HTML, with dynamic elements that can be changed on the client-side using scripting languages like JavaScript. But these same elements can become a huge security risk when they are left vulnerable to manipulation by outside actors.

If an attacker can alter these elements to make unauthorized queries, they can bypass any firewalls to access sensitive data.

2. Authorization Bypass

A vulnerability known as authorization bypass allows certain users to access information that should be beyond their authorization level. Since this is a very broad umbrella of vulnerabilities, it's no surprise that many levels and instances of cyberattacks fall under this category. 

Broken Object Level Authorization (BOLA) is already #1 on the OWASP API Security Top 10 list - and for good reasons. API providers do a great job of ensuring that users are authenticated to the API, so they want to make sure that legitimate users have access.

But the number one thing that's often overlooked is authorization, ensuring that user A can't access user’s B resources. And it's one thing to hide the resource IDs, but the important factor there is that user A should not be able to access, interact with, or alter user B’s resources - at all.

Corey Ball, Cybersecurity Consulting Manager & Author of "Hacking APIs"

The two most common subtypes of authorization bypass include:

• Lateral movement: accessing data of another account at the same privilege level
• Privilege escalation: accessing data that the current privilege level isn't supposed to have access to

Strong authorization and authentication protocols - such as oAuth or OpenID - should be implemented to prevent authorization bypass and protect your systems against this attack vector.

3. Failing to Handle Unconventional User Input

An attacker can trigger an unexpected response from your systems by providing inputs to an API that a developer failed to anticipate, potentially exposing sensitive data.

Many APIs lack the security controls that other attack vectors have in place, making them the equivalent of the Death Star's thermal exhaust port: a path to doom and destruction for businesses.

Corey Ball, Cybersecurity Consulting Manager & Author of "Hacking APIs"

Businesses have to be very careful when it comes to handling unconventional user input and meticulously test for all data types, including unexpected values and characters.

They can do this by running a series of fuzz tests to feed the systems with different kinds of random user input.

4. Putting Excessive Trust in Users

Many IT systems trust their authorized users too much, creating a host of security potential security vulnerabilities.

If an attacker can access the login credentials of real admin users - whether as a result of a phishing attack or by simply buying that data on the dark web - they can easily sneak in, access the database, and cause a data breach - similar to one led to the exposure of three billion Yahoo records.

To keep yourself safe and protected, you have to assume that every user is a potential security threat, whether authorized or not.

That's what the zero-trust security model is all about, ensuring that every user is properly authorized and authenticated - all while monitoring their behavior even after letting them in.

5. Domain-Specific Flaws

Domain-specific flaws are the weaknesses in your system that are only present in a specific area.

Unlike general vulnerabilities that affect your entire application, domain-specific flaws are only found within a particular module or function. 

This key aspect makes them harder to identify and fix because you need to deeply understand the objectives attackers may try to achieve by abusing domain-specific flaws.

The more information you have about what your end users are doing, the easier it is to identify and flag suspicious actions accurately. 

A good starting point would be utilizing your API management tool's analytics and reporting capabilities to identify and analyze usage patterns.

Read More: API Security Checklist: What You Need To Know

How to Prevent and Test for Business Logic Flaws in Your API Security

Effective API security testing is critical. And if we think back to the USPS data leak, that was tested a month before a leak of 60 million instances of private data. It’s not that you’re just testing APIs generically but that you’re using the right tools and techniques that will help your API security vulnerability management program to do a good job at preventing these sorts of attacks.

Corey Ball, Cybersecurity Consulting Manager & Author of "Hacking APIs"

Now that you know the most common types of business logic flaws, it’s time to do something about them.

Here are some tips for testing for business logic flaws in your API security:

1. Ensure that Your Test Cases Cover All Possible Scenarios

The first step towards ensuring that your API security is airtight is to craft as many test cases as possible to cover all possible attack scenarios.

The more attack scenarios you test against, the higher the chances of identifying the underlying business logic vulnerabilities.

That’s where you need a deep understanding of all aspects of your API to create test cases that actually move the needle.

APIs have direct access to sensitive data. They connect to your application servers, your microservices, and your database applications, so they have to be really secure. And a lot of APIs are overpermissioned - with some of them, you don’t even realize they’re probably leaking credentials.

Cecil Pineda, Co-Founder at CISO XC

2. Validate All User Input

Treat user input as a security threat by default. This approach entails validating all user input, regardless of where it’s coming from or who submits it.

That way, you’re protecting yourself from an entire layer of API vulnerabilities and drastically mitigate the risks related to insider threats.

All invalid input should be logged and eventually monitored to uncover potential chinks in your armor that can lead to a data breach.

The zero-trust security model has proven to be effective in reducing the number of cybersecurity incidents, so it’s a good idea to apply it to your APIs.

Read More: What Is API Privacy and How to Protect Your Sensitive Data

3. Improve Your API Documentation

Make sure that your APIs are adequately documented so that developers can understand how it works.

This will boost your adoption rates and help you catch any errors or inconsistencies in your business logic.

A well-documented API will make it easier for you to test for security vulnerabilities.

4. Monitor for Unusual Behavior and Review All Access Logs Regularly

API logging and monitoring are absolutely vital to protect your users from cyberattacks.

No system can ever be completely secure, so it’s crucial for your team to constantly track and analyze all auditable events - from failed logins to large transactions.

Some user actions may point you toward a critical business logic vulnerability, so eye your logs like a hawk.

5. Use Automated API Security Testing Tools

Automating your security testing is a great place to begin if you feel overwhelmed by this information or don't know where to begin.

The problem is that business logic flaws are incredibly difficult to identify and detect, even when having a team of developers at your disposal.

Often, your developers are the most expensive employees on your payroll.

Popular API testing tools lack the depth needed to truly protect your APIs because security is not their specialty, allowing you only to automate the execution of thousands of test cases that you still have to create manually.

That's where APIsec comes into play.

APIsec runs on every release, not just once or twice a year with the pen test cycle, constantly updating the playbooks and making sure that any new code gets evaluated.

APIsec is the only API security testing tool that automatically creates and executes thousands of test cases and actually makes it possible to identify business logic flaws based on the unique architecture of your API.

Our customers ask us what we’re doing to protect their sensitive data on Seismic, and once they see what we have done with APIsec, their confidence grows.

Tim Dzierzek, VP of Information Security

Request a demo today to learn about APIsec’s one-of-a-kind technology to keep your APIs and data safe.