Secure Code Review (SCR) : A7 — Missing Function Level Access Control

In the vast landscape of web application vulnerabilities, Missing Function Level Access Control stands out as a significant concern. It arises when applications do not adequately verify a user’s permissions before allowing access to certain functionalities. This oversight can lead to unauthorized users gaining access to sensitive operations or data.

In this blog, we will delve deep into the concept of Missing Function Level Access Control, provide illustrative examples, and furnish a comprehensive checklist for pinpointing this vulnerability during a secure code review.

Understanding Missing Function Level Access Control

Applications often have different roles, such as admin, user, or guest, each with its own set of permissions. Missing Function Level Access Control occurs when an application fails to validate whether the user has the necessary permissions to access a particular function.

For instance, consider a web application with a hidden URL for administrative functions. If an attacker guesses or discovers this URL, they might access the admin panel without any checks, leading to a potential breach.

Identifying Missing Function Level Access Control in Code Review

During a secure code review, the primary objective is to spot areas where the application might not be verifying user permissions adequately. Here’s what to focus on:

1. Unprotected Endpoints: Look for application endpoints or URLs that do not have any access control checks.
2. Client-Side Controls: If the application relies solely on client-side controls, such as JavaScript, to restrict access, it’s a potential vulnerability. Client-side controls can be easily bypassed.
3. Lack of Role Checks: Check if the application verifies the role of a user before granting access to a function.
4. Hardcoded Permissions: Look for hardcoded permissions or roles in the code, which can be a sign of inadequate access control.

Secure Code Review Checklist for Missing Function Level Access Control

Here’s a checklist to guide you when reviewing code for Missing Function Level Access Control:

1. Review All Endpoints: List all application endpoints and verify that each one has proper access control checks.
2. Bypass Client-Side Controls: If the application uses client-side controls for access, try bypassing them to see if the server enforces access controls.
3. Check Role-Based Access: Ensure that the application checks the user’s role before granting access to specific functions.
4. Look for Hardcoded Values: Review the code for hardcoded roles or permissions that could be exploited.
5. Test with Different User Roles: If possible, test the application with different user roles to ensure that each role can only access the functions they are permitted to.
6. Review Error Messages: Ensure that error messages do not reveal sensitive information about the application’s internal workings or provide clues about how to bypass access controls.

Mitigating Missing Function Level Access Control

To prevent vulnerabilities related to Missing Function Level Access Control, follow these best practices:

1. Server-Side Access Control: Always enforce access controls on the server-side. Never rely solely on client-side controls.
2. Role-Based Access Control (RBAC): Implement RBAC to define what each user role can and cannot do.
3. Avoid Hardcoding: Never hardcode roles or permissions in the code. Instead, fetch them from a secure configuration or database.
4. Regular Audits: Regularly audit user roles and permissions to ensure that they are correctly configured.
5. Use Framework Features: Many web development frameworks offer built-in features for access control. Use them to ensure a more secure implementation.

In conclusion, Missing Function Level Access Control is a vulnerability that can lead to significant security breaches if not addressed. By conducting a thorough secure code review and adhering to the best practices outlined above, you can significantly reduce the risk associated with this vulnerability. Regular monitoring, testing, and auditing are also crucial to ensure ongoing security.

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