OWASP Top 10 – A01: Broken Access Control Explained
Published
Learn how broken access control can lead to major security issues in web applications. This guide explains what it is, why it’s dangerous, common examples, and how to prevent it—all in simple language.
What is Broken Access Control?
Broken Access Control happens when a web application fails to properly restrict what users are allowed to do. It’s like giving someone the keys to a building and accidentally letting them open every door—even the ones they’re not supposed to.
For instance, a normal user might be able to access admin pages or view other users’ private data just by tweaking the URL or using browser tools. This kind of flaw is a serious security risk and is ranked #1 in the OWASP Top 10.
Why Is It Dangerous?
Access control defines who can do what within your system. If that control is broken, it can lead to:
- Unauthorized access to sensitive data
- Users gaining admin privileges
- Data modification or deletion by unauthorized users
- Full system takeover in extreme cases
These issues can lead to data breaches, legal trouble, customer trust loss, and financial damage.
Common Examples of Broken Access Control
1. Insecure Direct Object References (IDOR)
A user can access another person’s data by changing a value in the URL. For example, changing /user/123 to /user/124 may show someone else’s profile.
2. Missing or Weak Authorization Checks
The app doesn’t properly check if the user has permission to perform an action—like deleting data without being an admin.
3. Forced Browsing
Attackers manually access hidden pages (like /admin) that aren’t protected, but should be.
4. Privilege Escalation
Users increase their access level by exploiting flaws, going from “user” to “admin” without proper checks.
How to Prevent Broken Access Control
- Deny by default: Start with no access and only allow what's necessary.
- Use role-based access control (RBAC): Define roles and permissions clearly.
- Enforce access checks on the server: Don’t rely on client-side restrictions.
- Regular security testing: Use automated tools and manual checks to catch issues early.
- Avoid “security through obscurity”: Just hiding pages or links is not enough.
Real-World Case
In 2019, a major financial company suffered a breach because of broken access control. The attacker accessed private financial data simply by changing parameters in a request. This led to massive fines and loss of customer trust.
Final Thoughts
Broken access control is one of the most common and dangerous vulnerabilities in web security. Every developer and security team must ensure users can only do what they’re supposed to. By following best practices, you can protect your application—and your users—from serious harm.
