Access control is a fundamental aspect of cybersecurity that ensures users can only access resources and data that they are authorized to use. However, when access controls are improperly implemented, attackers can exploit these weaknesses to gain unauthorized access to sensitive information or perform actions beyond their privileges. This security flaw is known as Broken Access Control and is ranked as the #1 security risk in the OWASP Top 10.

What is Broken Access Control?

Broken Access Control occurs when an application fails to enforce proper restrictions on authenticated users, allowing unauthorized individuals to access or modify data they shouldn't be able to. This vulnerability arises due to misconfigured permissions, missing access controls, or flaws in authentication and authorization mechanisms.

Common Examples of Broken Access Control

• Privilege Escalation: A user with basic privileges manipulates application requests to gain administrative access.
• Unauthorized Data Access: Users accessing confidential data by modifying URLs, parameters, or API requests.
• Forced Browsing: Attackers directly access hidden pages or endpoints that lack proper authorization checks.
• Insecure Direct Object References (IDOR): Manipulating object identifiers to access resources belonging to other users.
• Bypassing Role-Based Access Control (RBAC): Exploiting vulnerabilities to perform actions restricted to higher privilege levels.

How Attackers Exploit Broken Access Control

Attackers often leverage simple techniques to exploit broken access control vulnerabilities. Some common attack methods include:

• URL Tampering: Modifying URL parameters to gain access to unauthorized resources. Example:

  https://example.com/user/profile?id=1001

  Changing the ID value to access another user's profile:

  https://example.com/user/profile?id=1002

• Modifying API Requests: Intercepting API calls using tools like Burp Suite to alter access control-related fields.
• Session Hijacking: Using stolen session tokens to impersonate authorized users.
• Client-Side Manipulation: Modifying JavaScript or local storage values to gain elevated privileges.

How to Prevent Broken Access Control

Mitigating broken access control requires a combination of secure coding practices, proper authorization mechanisms, and continuous security testing. Here are some key strategies:

• Implement Role-Based Access Control (RBAC): Restrict user actions based on predefined roles and permissions.
• Enforce Server-Side Authorization: Validate access controls on the backend, never relying solely on client-side enforcement.
• Use Secure Session Management: Implement proper session expiration, token validation, and prevent session fixation attacks.
• Apply the Principle of Least Privilege (PoLP): Grant users the minimum permissions necessary to perform their tasks.
• Regular Security Testing: Perform penetration testing and security audits to identify access control flaws.
• Log and Monitor Access Control Violations: Detect unauthorized access attempts through logs and real-time monitoring.

Real-World Example: The Facebook Vulnerability

In 2018, Facebook suffered a broken access control vulnerability that allowed attackers to steal **access tokens** of nearly 50 million accounts. The flaw was exploited through Facebook’s “View As” feature, enabling attackers to gain control over user sessions without requiring passwords. This incident highlighted the critical importance of **secure session management and access control validation**.

Conclusion

Broken Access Control is a severe security risk that can lead to unauthorized access, data breaches, and privilege escalation attacks. As it remains the top-ranked issue in OWASP’s security risks, organizations must prioritize implementing robust access control mechanisms. By enforcing strict authorization policies, conducting regular security assessments, and adopting best practices like Role-Based Access Control and Least Privilege, businesses can effectively mitigate the risks associated with this vulnerability.