The Biggest Risk in Your Application May Not Be a Technical Vulnerability

What Are Authorization Flaws?

There is often some confusion between authentication and authorization.

Authentication answers a simple question:

Who is the user?

Authorization, on the other hand, answers:

What can this user access?

Many applications correctly implement login, MFA, password recovery, and session management.

Yet they fall short when it comes to verifying whether that user actually has permission to access a given resource.

That is precisely where some of the most dangerous vulnerabilities found in modern pentests come from.

A Simple Example

Imagine a platform where customers can view their own orders.

When accessing a specific order, the application makes a request similar to this one:

GET /api/orders/1001
Authorization: Bearer eyJhbGc...

Everything works as expected.

The user receives the data for order 1001.

Now imagine they manually change the identifier:

GET /api/orders/1002
Authorization: Bearer eyJhbGc...

If the application returns information belonging to another customer, there is an authorization flaw.

No advanced technique was used.

No complex exploitation was needed.

Just a simple change to the resource identifier.

Why Is This Type of Flaw Still So Common?

Modern applications tend to grow quickly.

New features are added constantly, APIs are created, integrations are implemented, and different user roles start to coexist within the same environment.

Over time, keeping authorization controls consistent across every endpoint becomes a challenge.

Developers often implement validation only on the frontend.

The problem is that attackers do not use only the application's interface.

They interact directly with APIs, modify requests, and analyze how the backend behaves.

When validation does not happen on the server, the risk increases significantly.

The Problem Gets Even Worse in SaaS Environments

In multi-tenant applications, an authorization flaw can affect many customers at once.

Imagine a platform used by hundreds of different companies.

Each company should only be able to see its own data.

But if authorization controls are not implemented correctly, one customer may end up accessing information belonging to another customer.

Depending on the context, this can result in:

• Exposure of personal data
• Exposure of financial information
• LGPD violations
• Breach of contract
• Loss of customer trust
• Regulatory consequences

In many cases, this type of flaw represents a greater risk than the more "famous" vulnerabilities.

Why Do Automated Scanners Usually Miss This Problem?

Automated tools are extremely useful for identifying known vulnerabilities.

They can detect problems such as:

• SQL Injection
• XSS
• Insecure headers
• Vulnerable dependencies
• Misconfigurations

Authorization flaws, however, usually depend on context.

A scanner can identify that a given endpoint exists.

But it will hardly be able to understand whether user John should or should not have access to company Mary's data.

That kind of validation requires manual analysis, an understanding of the business rules, and testing performed with different user roles.

Broken Access Control in the OWASP Top 10

It is no coincidence that Broken Access Control holds a prominent position in the OWASP Top 10.

This type of problem keeps showing up frequently in modern applications, APIs, and SaaS platforms.

Beyond its high frequency, the potential impact tends to be significant.

In many scenarios, a single flaw is enough to expose information belonging to hundreds or thousands of users.

Signs That Your Application May Have This Type of Problem

A few signs tend to show up often:

• Sequential identifiers exposed in URLs or APIs
• Validation performed only on the frontend
• Administrative roles without proper segregation
• No authorization testing during development
• Multi-tenant environments without consistent validation

The presence of these factors does not necessarily mean a vulnerability exists.

However, they tend to significantly increase the attack surface.

How to Reduce the Risk?

A few practices go a long way in preventing this type of problem:

• Validate authorization on every endpoint
• Implement checks on the backend
• Apply the principle of least privilege
• Review permissions periodically
• Run manual authorization tests
• Perform pentests focused on business logic

The earlier these controls are built into the development cycle, the lower the likelihood of problems reaching the production environment.

Conclusion

Not every data leak happens because of an extremely sophisticated vulnerability.

Often the problem is something far simpler: letting users access resources they should not be able to access.

Authorization flaws remain one of the leading causes of data exposure in modern applications and frequently go unnoticed during development.

Security assessments focused on business logic help identify this type of problem before it is exploited by attackers or results in incidents involving customer data.