OWASP API Security - Broken Object Level Authorization

• OWASP
• Broken Object Level Authorization
• API Security

API Security Object Level Authorization

In the world of modern apps, APIs are the backbone—handling data, running the show, and unfortunately, making juicy targets for attackers. That’s why knowing API security inside-out isn’t just an option; it’s a must if you don’t wanna be the next data breach headline.

OWASP API Security - Broken Object Level Authorization

You’ve probably heard of OWASP’s Top 10 web app vulnerabilities, right? Well, APIs get their own API Security Top 10, and at the very top of the list? Broken Object Level Authorization (BOLA)—aka the hacker’s golden ticket to your sensitive data. Here’s the full hit list:

• Broken Object Level Authorization (BOLA)
• Broken User Authentication
• Excessive Data Exposure
• Lack of Resources & Rate Limiting
• Broken Function Level Authorization
• Mass Assignment
• Security Misconfiguration
• Injection Attacks
• Improper Asset Management
• Insufficient Logging & Monitoring

Most of these can mess up any part of your app, but APIs are often where they hit the hardest. Let’s break down BOLA and why it’s the #1 enemy for APIs.

What’s the Deal with Broken Object Level Authorization?

APIs often rely on object identifiers, and when they don’t enforce strict access control, attackers can snatch data they have zero business accessing. It’s a problem across REST, SOAP, GraphQL—you name it.

Here’s a real-world mess-up: Let’s say an API exposes user payment info via user_id:

https://api.example.com/v1.1/users/payment/show?user_id=12

If this API doesn’t double-check who’s asking, anyone who figures out a valid user_id can waltz in and steal payment details. All it takes is some guessing or brute-forcing IDs to start a data heist.

Some APIs use object IDs instead of user IDs, which makes things worse. Check this out:

https://api.example.com/v1.1/messages/show?id=1337

Without proper access control, an attacker can cycle through IDs (id=1338, id=1339, etc.) and pull everyone’s messages. That’s BOLA in action—giving unauthorized users access to whatever they want just by tweaking an ID.

But wait—it gets worse. If an attacker can also update, delete, or create records, the damage jumps to a whole new level. In GraphQL APIs, for example, changing the ID in a mutation request could let someone edit or wipe out someone else’s data.

Why is This a Nightmare?

The level of chaos depends on what’s exposed. If an API leaks PII (Personally Identifiable Information), credentials, or financial details, attackers can:

• Scrape user data in bulk
• Hijack accounts
• Sell stolen data or commit fraud

Picture this: an eCommerce API leaks bank details and addresses. An insurance API leaks policyholder info. A healthcare API exposes medical records. See where this is going? Total disaster mode.

Locking Down Object Level Authorization

To shut down BOLA, APIs need to validate user access on every request. That means:

• Using access tokens instead of trusting user input (no user_id in the URL, please)
• Checking permissions at the object level (just because you’re logged in doesn’t mean you can see everything)
• Using unpredictable, secure object IDs instead of plain numeric ones

For example, switching from:

https://api.example.com/v1.1/messages/show?id=1337

to something like:

https://api.example.com/v1.1/messages/show?id=d0c240ea139206019f692d

makes brute-forcing way harder. But don’t rely on just that—always enforce access control.

Also, random IDs won’t save you if your API blindly trusts requests. If an attacker snags a valid ID, they’re still in. That’s why strict authentication & authorization checks matter more than anything.

Final Thoughts

If you’re building or securing APIs, Object Level Authorization should be at the top of your checklist. Even with strong access controls, there are other attack vectors, so never sleep on security.

APIs run the internet, but if they’re not locked down properly, they open the door for hackers. Time to fix that.

Stay secure. 🔥