Introduction to Access Control
Access control serves as a fundamental security mechanism that governs who can access specific resources on a system and what actions they can perform. At its core, access control ensures that unauthorized individuals are prevented from accessing sensitive data or performing critical operations. It acts as a barrier between legitimate users and potentially harmful actions by enforcing rules regarding who has permission to do what.
Access control systems rely on two primary components:
Authentication:
This verifies the identity of the user. It ensures that the individual attempting to access resources is who they claim to be. Authentication can involve passwords, multi-factor authentication (MFA), biometric verification, or other forms of identity proofing.
Session Management:
Once authenticated, session management ensures that the user’s actions are tracked and controlled over time. It maintains a seamless user experience while preventing unauthorized access during the session. Secure session management ensures the user does not have to re-authenticate for every interaction, but still enforces session-specific permissions.
Together, these components ensure that access is granted only to those who meet the defined criteria, based on their role, credentials, and session state.
Types of Access Control
Access control can broadly be categorized into several models:
- Role-Based Access Control (RBAC):
Access is granted based on roles assigned to users. For example, an admin might have full access to all features, while a regular user may be restricted to only specific sections. - Discretionary Access Control (DAC):
In DAC, the resource owner defines who has access to the resource. This model is commonly used in personal file systems but poses risks when not properly managed. - Mandatory Access Control (MAC):
MAC enforces access based on security labels assigned to resources and users. For example, in military systems, users are assigned clearances, and access is granted based on matching security labels. - Attribute-Based Access Control (ABAC):
Access decisions are made based on attributes such as the user’s location, device type, time of access, etc.
Common Access Control Vulnerabilities
Access control vulnerabilities occur when security mechanisms fail to protect resources properly, allowing unauthorized access or actions. Below are some of the most common types:
1. Privilege Escalation
Privilege escalation occurs when a user gains access to higher privileges than intended. This can be divided into two main categories:
- Vertical Privilege Escalation:
A lower-level user gains administrative privileges by exploiting flaws in the access control mechanisms. This could involve exploiting vulnerabilities in systems where permissions aren’t properly segregated. - Horizontal Privilege Escalation:
A user accesses resources or functions assigned to another user at the same level of privilege. For instance, an attacker gains access to another user’s account without higher-level privileges.
2. Insecure Direct Object References (IDOR)
An IDOR vulnerability occurs when attackers directly access resources via modified parameters in the URL, such as id=123
being changed to id=456
. This type of vulnerability allows attackers to access unauthorized data, edit records, or manipulate resources without appropriate permissions.
Example: If a user can change ?user=123
to ?user=456
, they might gain access to another user’s account or data.
3. Access Control List (ACL) Issues
Access control lists (ACLs) are used to define permissions on files, directories, or other resources. Misconfigured or outdated ACLs can inadvertently expose resources to unauthorized users. For example, if an administrator incorrectly configures an ACL, they might unintentionally allow access to files or resources intended only for specific roles.
4. Authentication Bypass
Weak authentication mechanisms, such as easily guessable passwords, insecure session tokens, or lack of MFA, allow attackers to bypass authentication altogether and gain unauthorized access.
Practical Testing Methodology
To effectively identify access control vulnerabilities, follow these steps during penetration testing:
- Create Target and Victim Accounts:
Set up two accounts on the target website:- Target account: For simulating attacks.
- Victim account: To mimic real user access.
- Use Tools Like Burp Suite:
Utilize Burp Suite to intercept and analyze requests/responses, looking for parameter manipulations and access control flaws.
Lab Scenarios and Testing Strategies
- Lab 1: Unprotected Admin Functionality
- Search for hidden admin panels that lack proper authentication.
- Test functionalities such as executing admin commands or uploading shells to demonstrate the impact of this vulnerability.
- Lab 2: Admin Functionality with Unpredictable URLs
- If the admin panel URL is not straightforward, inspect the source code to identify hints about its location.
- Identify patterns that suggest admin functionality and test access control.
- Lab 3: User Role Controlled by Request Parameters
- Inspect login requests and responses.
- Modify parameters such as
role
orprivilege
in intercepted requests to escalate permissions.
- Lab 4: User Role Modification via User Profile
- Log in as a normal user and analyze requests.
- Look for editable fields like
role_id
oruser_id
that can be manipulated to switch roles or access unauthorized accounts.
- Lab 5: User ID Controlled by Request Parameters
- Experiment with replacing your
user_id
or profile link with another user’s ID to test for horizontal privilege escalation.
- Experiment with replacing your
- Lab 6: User ID with Unpredictable Patterns
- If IDs are not sequential or predictable, explore profiles to identify ID formats and replace your ID with a victim’s ID to test unauthorized access.
- Lab 7: User ID with Password Disclosure
- Monitor intercepted requests for password leaks in responses or source code.
- Use these disclosures to validate the presence of IDOR vulnerabilities.
- Lab 8: Exploiting IDOR
- Alter resource identifiers in requests to access or modify unauthorized data, such as downloading files or viewing another user’s profile.
- Lab 9: Referer-Based Access Control
- Capture requests that alter user roles or permissions.
- Manipulate cookies or inject new user details to verify bypass scenarios.
- Lab 10: Multi-Step Process with Missing Access Controls
- Analyze multi-step workflows, such as user role changes.
- Capture each step and test with modified cookies or parameters.
- Lab 11: Circumventing Method-Based Access Control
- Change HTTP request methods (e.g.,
POST
toGET
orPOSTX
) to test bypassing method-based access restrictions.
- Change HTTP request methods (e.g.,
- Lab 12: Data Leakage in Redirects
- Intercept login requests and analyze responses for sensitive data leaks.
- Replace user details with victim account information to test access.
- Lab 13: Password Disclosure via User ID
- Inspect intercepted requests for password or sensitive data leakage when modifying user IDs.
- Exploit these disclosures to take over accounts.