Broken access control

Broken Access Control is a significant security vulnerability where attackers are able to gain access to resources, data, or systems that they should not have access to. This vulnerability often stems from improper enforcement of restrictions on what authenticated users are allowed to do or see. Broken access control is consistently ranked as one of the most critical security risks, according to the OWASP Top 10.

In this blog post, we’ll explore what Broken Access Control is, why it’s so dangerous, and provide some real-world examples, along with preventive measures.

What is Broken Access Control?

Access control refers to the mechanisms that restrict who can access a resource in a system. This can involve limiting access based on a user’s role, permission levels, or context. Broken access control occurs when these restrictions are improperly implemented or fail to be enforced effectively, allowing unauthorized users to bypass them.

Broken access control can happen in many ways, including:

• Insecure Direct Object References (IDOR): Users being able to access objects (like files or records) they shouldn’t be able to, simply by modifying a URL or a parameter.
• Role-based Access Control (RBAC) issues: Users with lower privileges can access areas or data intended for higher-privileged users.
• Missing or Improperly Configured Authentication: Where access checks are skipped or improperly implemented.

Real-World Examples

Example 1: Insecure Direct Object Reference (IDOR)

Imagine you have an application where users can view their personal profile. Each user profile is identified by a unique numeric ID in the URL, such as:

<https://example.com/profile?user_id=12345>

In a properly secured system, a user should only be able to access their own profile. However, if access control is improperly configured, an attacker could simply modify the user_id parameter in the URL and access the profiles of other users, like so:

<https://example.com/profile?user_id=12346>

In this case, an attacker could view sensitive information of other users, such as their names, addresses, or account details.

How to Fix: Always ensure that access control checks are performed on the server-side, even if the user has authenticated. Never rely solely on URL parameters or client-side checks.

Example 2: Missing Role-Based Access Control (RBAC)

Consider a web application with an admin panel, where only administrators should be able to view and modify user data. A regular user is able to log in and navigate to an admin page, such as:

<https://example.com/admin/users>

If the application doesn’t properly check the user’s role or permissions before loading the page, the regular user might be able to view sensitive data, such as other users’ personal information or even change user privileges.

How to Fix: Always ensure that role-based access control is implemented in the backend, and verify that the authenticated user has the correct role and permissions before granting access to sensitive features.

Example 3: Lack of Authorization in APIs

Many modern applications rely heavily on APIs to interact with users and other systems. A common mistake in API development is failing to implement proper authorization checks. For example, an API might expose endpoints like:

GET /api/users/12345

If the server doesn’t verify that the currently authenticated user is allowed to access the data for user_id=12345, an attacker could craft a request to view someone else’s data:

GET /api/users/67890

How to Fix: Ensure that every API endpoint performs strict authorization checks, and never expose sensitive data without proper authentication and authorization mechanisms in place.

Why Broken Access Control is Dangerous

Broken access control vulnerabilities are dangerous because they allow attackers to bypass the security model of an application. This can result in:

1. Data Breach: Sensitive user information (e.g., personal, financial, medical) can be exposed to unauthorized parties.
2. Privilege Escalation: Attackers can elevate their privileges to access areas they should not have permission to, leading to data modification, deletion, or compromise of the entire system.
3. Reputation Damage: If a breach occurs due to broken access control, it can severely damage the trust between the company and its users, leading to lost business and regulatory consequences.

How to Prevent Broken Access Control

1. Implement Strong Authentication and Authorization:
   • Always enforce authentication and authorization checks on the server-side. Don’t rely on client-side restrictions or parameters alone.
   • Use secure session management practices to prevent session hijacking or fixation.
   • Leverage multifactor authentication (MFA) for sensitive actions and administrative access.
2. Apply the Principle of Least Privilege:
   • Ensure users and services only have the minimum permissions necessary to perform their tasks. This minimizes the potential damage if an account is compromised.
   • Ensure role-based access control (RBAC) is properly implemented, with a clear separation of roles (e.g., admin, user, guest) and permissions assigned accordingly.
3. Perform Consistent Input Validation:
   • Never trust user input. Ensure that every request, whether through URLs, HTTP headers, or body parameters, is validated against a set of expected values.
   • Use parameterized queries for database operations to prevent unauthorized data manipulation.
4. Use Secure API Endpoints:
   • APIs should always validate user permissions and roles before providing any data or performing any actions.
   • Implement token-based authentication, such as OAuth or JWT, and include access control checks for every API request.
5. Implement Access Control Lists (ACLs):
   • Use ACLs to map what actions each user role can perform on specific resources. Ensure that every resource has a defined access control list, and restrict access accordingly.
6. Test for Broken Access Control:
   • Regularly perform security testing, including automated vulnerability scans and manual penetration testing, to identify and fix broken access control vulnerabilities.
   • Tools like OWASP ZAP and Burp Suite can help identify security flaws in web applications.

Conclusion

Broken Access Control is one of the most common and dangerous security vulnerabilities that can lead to severe breaches of sensitive data, privilege escalation, and even full system compromise. It is essential for developers and security teams to understand the nuances of access control and ensure they implement proper measures to safeguard their systems.

By following best practices such as implementing strong authentication and authorization, applying the principle of least privilege, and thoroughly testing your application, you can significantly reduce the risk of Broken Access Control vulnerabilities.