Understanding and Identifying Broken Object Level Authorization (BOLA) Vulnerabilities in APIs

Understanding Broken Object Level Authorization (BOLA) in APIs

Introduction

Broken Object Level Authorization (BOLA) is a critical security vulnerability affecting APIs. This flaw allows attackers to access data or actions that they are not authorized to access by simply manipulating resource identifiers within API requests. This article will explore the mechanics of BOLA, its potential impacts, and how to effectively identify and mitigate such vulnerabilities.

What is BOLA?

BOLA, also known as Insecure Direct Object Reference (IDOR), occurs when an application does not correctly verify that a user is authorized to access a specific resource. This issue arises from the assumption that users will only access resources they own, without validating this assumption server-side.

Steps to Identify BOLA Vulnerabilities

1. Account Setup:

   • Create UserA Account: Start by registering a user account (UserA) on the application.

2. Request Exploration:

   • Use the API as UserA: Interact with the API using UserA’s account to discover requests that involve resource IDs (e.g., account IDs, user IDs).
   • Document Requests: Record API requests that require authorization, noting the endpoints and resource identifiers.

3. Second Account Creation:

   • Create UserB Account: Register a second user account (UserB).

4. Token Switch Test:

   • Obtain a Valid UserB Token: Secure a valid authentication token for UserB.
   • Attempt Unauthorized Access: Try to access UserA’s resources using UserB’s token. Conversely, use UserA’s token to access UserB’s resources.

Example of a BOLA Attack

1. Identify an Interesting Request:

   • Focus on requests involving complex resource IDs such as vehicle IDs, account numbers, etc.

2. Capture Request:

   • Use tools like Burp Suite to capture the request made by UserB when accessing their own resource.

3. Perform BOLA Attack:

   • Token Manipulation: Replace UserB’s token with UserA’s token in the captured request.
   • Request Submission: Attempt to execute the modified request using UserA’s token.

4. Successful Exploitation:

   • Validation: Confirm the successful execution of the request, demonstrating access to UserB’s data with UserA’s token.
   • Data Capture: Extract sensitive information such as GPS location, vehicle ID, and full names belonging to UserB.

Practical Example

Consider the following scenarios highlighted in the table:

• Predictable ID:

  • Valid Request: GET /api/v1/account/2222 with UserA_token
  • BOLA Test: GET /api/v1/account/3333 with UserA_token

• ID Combo:

  • Valid Request: GET /api/v1/user/UserA/data/2222 with UserA_token
  • BOLA Test: GET /api/v1/user/UserB/data/3333 with UserA_token

• Group ID:

  • Valid Request: GET /api/v1/group/CompanyA with UserA_token
  • BOLA Test: GET /api/v1/group/CompanyB with UserA_token

Each scenario demonstrates how altering the resource ID while maintaining the same token can lead to unauthorized data access, a hallmark of BOLA.

Additional Insight: Excessive Data Exposure

BOLA vulnerabilities often go hand-in-hand with excessive data exposure. This occurs when the API returns more data than necessary, providing a rich target for attackers. For example, an API endpoint might inadvertently expose user details such as email addresses, full names, or sensitive configuration data.

Mitigation Strategies

To protect against BOLA, consider the following measures:

• Implement Robust Access Controls:

  • Verify authorization for each resource access request server-side, ensuring users can only access resources they are permitted to.

• Use Non-Predictable IDs:

  • Employ UUIDs or other non-sequential identifiers to make it harder for attackers to guess valid resource IDs.

• Least Privilege Principle:

  • Grant users the minimum level of access necessary for their role, reducing potential exposure.

• Regular Audits and Testing:

  • Conduct regular security audits and penetration testing to identify and address BOLA vulnerabilities before they can be exploited.

Conclusion

BOLA represents a significant threat to API security, allowing attackers to bypass authorization controls and access unauthorized resources. By understanding the mechanisms behind BOLA and implementing robust security practices, organizations can protect their APIs from such vulnerabilities, ensuring data confidentiality and security.

Checklist for Identifying and Mitigating BOLA

• Create and explore accounts for testing (UserA and UserB).
• Capture and analyze API requests to identify authorization mechanisms.
• Test for unauthorized access by manipulating resource identifiers.
• Validate findings and secure identified vulnerabilities.
• Continuously monitor and update security measures to protect against evolving threats.

By following these steps and implementing recommended security practices, organizations can effectively safeguard their APIs against BOLA vulnerabilities, protecting sensitive data and maintaining trust with their users.