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Resources > Blog >
Broken Access Control: Attack Examples and 4 Defensive Measures

Broken Access Control: Attack Examples and 4 Defensive Measures

Nedim Marić

What Is a Broken Access Control Vulnerability? 

Broken access control vulnerability is a security flaw that allows unauthorized users to access, modify, or delete data they shouldn’t have access to. This vulnerability is considered one of the most critical web application security risks. It occurs when an application fails to properly enforce access controls, allowing attackers to bypass authorization and perform tasks as if they were a legitimate user.

This vulnerability can exist in various forms, such as inadequate session management, improper enforcement of role-based access controls, or insecure direct object references (IDOR). Developers and security professionals have a responsibility to understand the risks associated with broken access control and take necessary steps to mitigate them.

The Open Web Application Security Project (OWASP) lists broken access control as the #1 critical web application security risk (according to the OWASP Top 10 list, updated 2021).

This is part of a series of articles about unauthorized access

In this article:

The Impact and Risk of Broken Access Controls 

The impact of broken access control can be catastrophic for organizations. Unauthorized access to sensitive data can lead to data breaches, identity theft, financial loss, and damage to a company’s reputation. In worst-case scenarios, it can even result in total system compromise where attackers gain complete control over the system.

The risk associated with broken access control is high because it directly affects the confidentiality, integrity, and availability of data. An attacker exploiting this vulnerability can potentially access, modify, or delete any data on the system. This includes user data, system data, application data, and more. The larger the system and the more sensitive the data, the higher the risk.

Broken access control is a vulnerability that can’t be ignored, and organizations must take proactive steps to identify and mitigate it. This involves regular security testing, proper design and implementation of access controls, and continuous monitoring and updating of security measures.

Examples and Types of Broken Access Control Attacks 

There are several ways in which an attacker can exploit broken access control vulnerabilities: 

URL Manipulation

URL manipulation is a straightforward method used by attackers to exploit broken access control vulnerabilities. This involves changing the URL in an attempt to bypass access controls and gain unauthorized access to sensitive data or functionality. If the application doesn’t properly enforce access controls, an attacker can simply modify the URL to access restricted resources.

For instance, consider a URL that includes the user’s ID: An attacker could change the ID in the URL to to access another user’s data. If the application doesn’t verify the user’s access rights before serving the requested data, it’s vulnerable to a broken access control attack.

Exploiting Endpoints

Endpoints are the points of interaction between an application and the rest of the system. These could be APIs, microservices, or any other service that the application relies on. If these endpoints are not properly secured, they can be exploited by attackers to bypass access controls.

Attackers can identify unprotected endpoints through various methods, such as scanning the network, analyzing the application code, or even guessing the endpoint URLs. Once they find an unprotected endpoint, they can send unauthorized requests to access, modify, or delete data.

Elevating User Privilege

Another common method used by attackers is privilege escalation. This involves gaining unauthorized access to a lower-level account and then escalating the privileges of that account to gain access to more sensitive data or functionality.

For example, an attacker might first gain access to a regular user account through some other vulnerability, such as weak passwords. Once inside, they can exploit broken access control vulnerabilities to elevate their privileges and gain access to an admin account. With admin access, they can perform any action on the system, including accessing and modifying sensitive data.

Insecure Direct Object References (IDOR)

Insecure Direct Object References (IDOR) is a type of broken access control vulnerability where an application exposes direct references to internal implementation objects. This can include database keys, file paths, or any other internal reference. If an attacker can guess or brute-force these references, they can bypass access controls and access sensitive data directly.

For example, consider an application that uses database keys in its URLs: An attacker could change the key in the URL to access another object, which might contain sensitive data. If the application doesn’t verify the user’s access rights before serving the requested data, it’s vulnerable to an IDOR attack.

4 Ways to Prevent Broken Access Control 

1. Implementing the Principle of Least Privilege

The Principle of Least Privilege (PoLP) is a cybersecurity concept in which a user is given the minimum levels of access necessary to perform their job functions. The principle is used to prevent users from accessing information or commands that they do not need for their job, thereby preventing them from damaging the system or accessing confidential information.

Implementing PoLP begins with identifying the various roles within your organization and defining their access needs. Each role should only have access to the resources necessary to fulfill their job responsibilities—no more, no less. This principle extends beyond just human users to include processes, systems, and devices.

Next, it is essential to continually review and update these roles to reflect changes within the organization. As employees leave, join, or shift positions within the company, their access needs will change. Regularly reviewing these roles ensures that access permissions always align with each role’s current needs.

2. Secure Session Management and Authentication Controls

Secure session management and authentication controls are another critical aspect of preventing broken access control. These measures ensure that only authorized users can access your system and that they can only access the parts of the system that they need to.

Secure session management involves creating a unique session for each user when they log in and destroying that session when they log out or after a period of inactivity. This prevents unauthorized users from hijacking a user’s session and gaining access to their account.

Authentication controls verify that users are who they claim to be. This is usually done through a combination of usernames and passwords, but can also involve other methods such as biometrics or security tokens.

It is also important to implement multi-factor authentication (MFA), which requires users to provide two or more verification factors to gain access. MFA reduces the risk of an attacker gaining access to the system even if they manage to obtain a user’s password.

3. Regular Access Control Audits and Reviews

Another best practice is to conduct regular access control audits and reviews. These audits should be comprehensive and cover all aspects of your access control system, including the roles and privileges assigned to each user, how access rights are granted and revoked, and the security measures in place to protect your access control system.

Regular audits help to ensure that your access control policies are being followed and that there are no security gaps that could be exploited. They also provide an opportunity to identify any unnecessary or excessive access rights that may have been granted, allowing you to revoke these rights and reduce your system’s attack surface.

Additionally, regular reviews of your access control system can help you identify any trends or patterns that could indicate a security issue. For example, if a particular user is repeatedly attempting to access resources they should not have access to, this could indicate that they are trying to exploit a weakness in your access control system.

4. Proper Error Handling and Logging

Proper error handling and logging are another crucial aspect of preventing broken access control. Errors can provide valuable information about potential security vulnerabilities in your system, and logging these errors can help you identify and address these vulnerabilities before they can be exploited.

When an error occurs, your system should respond in a way that does not reveal any sensitive information. For example, if a user attempts to access a resource they do not have permission for, the system should not reveal the existence of that resource or the reason for the denial of access. Instead, it should simply inform the user that they do not have permission to access the requested resource.

Logging involves recording the details of each action taken within your system. This includes successful and unsuccessful login attempts, changes to access rights, and attempts to access restricted resources. These logs can then be analyzed to identify unusual or suspicious behavior.

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