Understanding Broken Function Level Authorization and How to Prevent It in Your APIs

A Comprehensive Guide to OWASP API5 and Function Level Authorization Vulnerabilities | Karthikeyan Nagaraj

Introduction:

APIs have become an essential part of modern web applications, enabling them to interact with each other and share data seamlessly.
However, with the increasing use of APIs, the risks associated with them have also increased, and one of the most common vulnerabilities is Broken Function Level Authorization.
This vulnerability occurs when an API lacks proper access control measures, allowing an attacker to gain access to unauthorized resources or functions.
In this article, we’ll explore OWASP API5 and Function Level Authorization Vulnerabilities in detail and provide tips on how to prevent them.

Working Principle of Broken Function Level Authorization:

Function Level Authorization is a security mechanism that controls access to different functions or resources in an API.

In a well-designed API, each function or resource should have a specific access level that corresponds to the user’s role or privileges. When an API lacks proper access control measures, an attacker can exploit this vulnerability by manipulating requests and accessing unauthorized resources or functions. Attackers can exploit this vulnerability in various ways, including:

Changing or removing parameters in a request to access unauthorized functions or resources.
Using a valid user session or token to gain access to unauthorized resources or functions.
Modifying the request method (e.g., GET, POST) to perform actions that are not allowed for that user.

How to Exploit Broken Function Level Authorization:

To exploit Broken Function Level Authorization, attackers use various techniques that include:

Intercepting and modifying API requests using tools like Burp Suite or Postman.
Trying different values for request parameters to see which ones grant access to unauthorized resources or functions.
Modifying the API client code to bypass authorization checks.
Reusing a valid user session or token to gain access to unauthorized resources or functions.

Preventions of Broken Function Level Authorization:

To prevent Broken Function Level Authorization, you should implement proper access control measures in your API. Some of the best practices include:

Implementing Role-Based Access Control (RBAC) to control access to different functions or resources based on the user’s role or privileges.
Validating input parameters to ensure that they contain only allowed values and are not vulnerable to injection attacks.
Implementing Multi-Factor Authentication (MFA) to prevent unauthorized access to user accounts.
Using secure session management to prevent session hijacking or fixation attacks.
Implementing rate limiting to prevent brute force attacks on login or password reset functions.
Using a Content Security Policy (CSP) to prevent Cross-Site Scripting (XSS) attacks.
Conducting regular security assessments and penetration testing to identify and remediate vulnerabilities.

Conclusion:

In conclusion, Broken Function Level Authorization is a serious vulnerability that can lead to unauthorized access to sensitive resources or functions in an API.
To prevent this vulnerability, it’s crucial to implement proper access control measures and follow best practices for API security.
By implementing role-based access control, input validation, multi-factor authentication, secure session management, rate limiting, and content security policy, you can minimize the risk of Broken Function Level Authorization and protect your API from attackers.
Additionally, conducting regular security assessments and penetration testing can help identify and remediate vulnerabilities before they are exploited by attackers.