Broken Access Control: A Serious Web Vulnerability
Published: 2023-08-06 15:46:21

by [Vincent Chosen](https://blog.openreplay.com/authors/vincent-chosen)

<blockquote><em>In today's digital world, where web applications and software systems, in general, have become an integral part of our lives, ensuring the security and integrity of these systems is of the utmost importance. A key factor that stands out among the many security concerns that developers and organizations face is **Access Control**, the foundation of strong web security, determining who has access to specific resources or can perform specific actions within a system. This article will explain what Broken Access Control is, what causes it, its consequences, and how to prevent such vulnerabilities from affecting the security of your web applications.</em></blockquote>


Access Control acts as the security guard, carefully regulating permissions and privileges to prevent an unauthorized user from compromising sensitive data, tampering with vital operations, or gaining improper advantages. It's a mechanism that distinguishes between a legitimate user and a malicious intruder, ensuring that the right people have access to resources while keeping the wrong hands away.

However, despite its critical role in web security, Access Control is not resistant to vulnerabilities. One particular threat that affects many systems is "**Broken Access Control**". This security vulnerability occurs when its mechanisms are misconfigured, improperly implemented, or fail to account for edge cases. In essence, it allows attackers to evade the intended restrictions, granting them unauthorized access and potentially resulting in serious security breaches.

Understanding the complexities of Broken Access Control and implementing best practices can help you protect your digital assets, user data, and the integrity of your web-based systems.

Let's get to it.

## What is Broken Access Control
Broken Access Control is a security flaw that occurs when the access control mechanisms within a web application have weaknesses, are misconfigured, or are disregarded, allowing unauthorized individuals to gain unauthorized access to restricted resources or perform actions beyond their authorized privileges. In simple terms, the system fails to enforce appropriate user access restrictions, allowing unauthorized users to access sensitive data, manipulate functionalities, or elevate their privileges within the application.

The term "broken" refers to access control mechanisms that are not working properly or have been compromised somehow. This can happen for a variety of reasons, which we'll go over later in this article.

When there are Broken Access Control vulnerabilities in a web application, attackers can use them to perform malicious activities. Therefore, developers and organizations must identify and address Broken Access Control vulnerabilities to ensure the security and integrity of their web applications.

## Examples of Broken Access Control
Here are some examples of Broken Access Control vulnerabilities found in web applications:
1. **[Horizontal and Vertical Access Control](https://portswigger.net/web-security/access-control#:~:text=Horizontal%20access%20controls%20are%20mechanisms,resources%20of%20the%20same%20type.)**: Horizontal Access Control occurs when a normal user has access to a restricted resource or performs an action that should only be performed by someone else with a different user role and permissions. For example, a non-privileged user gaining access to administrative functions or sensitive data intended for privileged users. In Vertical Access Control, on the other hand, an authorized user can increase their privileges or gain access to resources beyond their intended authorization level. For instance, a user with limited access exploits a vulnerability to gain administrative privileges.
2. **Direct Object Reference:** This vulnerability occurs when a web application exposes internal references to resources in its URLs or parameters, such as database identifiers or file paths. Attackers can use these references to gain unauthorized access to resources or data. For example, changing a URL parameter to access another user's sensitive information.
3. **[Insecure Direct Object References (IDOR)](https://portswigger.net/web-security/access-control/idor)**: IDOR occurs when an application fails to validate or authorize user access to resources, similar to direct object references. This vulnerability enables attackers to directly manipulate references or use sequential identifiers to gain access to resources they should not have.
4. **Invalidation of Session Tokens**: When a user logs out of an application, the session id token should be invalidated to prevent unauthorized access. On the other hand, an attacker could obtain or reuse an active session token to gain unauthorized access if the application fails to properly invalidate session id tokens.
5. **Insecure Function-Level Authorization**: This vulnerability occurs when access control checks are not applied consistently across the functions or actions of an application. It enables attackers to get around access controls for specific functions, allowing them to gain unauthorized access or perform actions.

These are just a few examples of Broken Access Control vulnerabilities that can exist in web applications.

## Common Causes of Broken Access Control
* **Inadequate Security Testing**: Inadequate security testing, such as failing to conduct thorough access control assessments, can result in undetected vulnerabilities. Weaknesses in access control mechanisms may go undetected if proper testing is not performed, resulting in broken access control.
* **Inadequate or Misconfigured Access Control Policies**: Inadequately defined or inconsistent access control policies can result in Broken Access Control. Unauthorized access to resources can occur if the policies are too permissive or are not accurately aligned with the intended user roles and permissions.
* **Improper Access Control Implementation**: When access control mechanisms are not implemented correctly, such as missing or inadequate checks, vulnerabilities can arise. For example, failing to validate user inputs or verify user permissions can result in unauthorized access.
* **Inadequate User Input Validation**: Inadequate user input validation allows attackers to manipulate requests and gain unauthorized access to restricted resources. Attackers may break access controls and inject malicious code without proper validation.
* **Lack of Session Management**: Inadequate session management may give rise to Broken Access Control. Attackers can exploit session tokens if they are not properly managed, are not invalidated upon logout, or are vulnerable to session fixation attacks.
* **Insecure Default Settings or Configurations**: Using insecure default settings or configurations can introduce vulnerabilities. For example, if default user accounts or authorizations have excessive privileges or default access controls are overly permissive, unauthorized access might occur.
* **Inadequate Verification of User Permissions**: Unauthorized access can also occur if user permissions are not consistently and thoroughly checked throughout the application's functions or actions. Inadequate or missing permission checks can allow users to perform actions they are not authorized to perform.

## Consequences of Broken Access Control
* **Reputational Damage**: When a web application suffers from security flaws such as Broken Access Control, it can harm the organization's reputation and trustworthiness. News of a data breach or unauthorized access can quickly spread, resulting in a loss of customer trust, decreased user adoption, and potential brand image damage.
* **Financial Loss and Legal Liabilities**: Organizations may incur financial losses due to a breach in access control. Financial fraud, theft, or regulatory penalties can result from breaches involving unauthorized access to sensitive financial data or payment information. Furthermore, organizations may face legal liability if they fail to adequately protect user data or violate data protection regulations.
* **Data Modification or Manipulation**: Broken Access Control can allow attackers to manipulate or modify data within the application. They may tamper with records, change settings, or alter critical information, resulting in data integrity problems, incorrect results, or even system failure.
* **Account Takeover and Privilege Escalation**: Successful exploitation of Broken Access Control can allow attackers to elevate their privileges within the application. They can gain administrative access or impersonate other users with higher privileges. This can result in the attacker gaining unauthorized control of the application, allowing him to perform malicious actions, compromise other accounts, or manipulate the system.
*  **Violations of Compliance**: Many industries and jurisdictions have regulations and compliance standards to protect user data and ensure web application security. Organizations may face legal consequences, fines, or other penalties if Broken Access Control vulnerabilities result in noncompliance with these regulations.
*  **Service and Availability Disruption**: In some cases, attackers may use Broken Access Control vulnerabilities to disrupt the web application's or its services' availability. They may launch denial-of-service attacks, change critical settings, or manipulate resources, resulting in service disruptions, system downtime, or a poor user experience.

To avoid these consequences, organizations must prioritize strong access control measures, conduct regular vulnerability assessments on their applications, and address any identified issues as soon as possible to ensure the security, integrity, and availability of their web applications and the data they handle.


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## Steps to Prevent Broken Access Control
Strong access control measures are required to prevent Broken Access Control vulnerabilities in web applications. Here are some important steps to take to help prevent Broken Access Control:
* **Implement [Role Based Access Control (RBAC)](https://www.digitalguardian.com/blog/what-role-based-access-control-rbac-examples-benefits-and-more) Model**: Define distinct roles and permissions for various user types in your application. Assign each user the appropriate role based on their responsibilities and limit their access accordingly. Implement RBAC mechanisms to effectively enforce and manage these roles.
* **Strong Authentication and Authorization Mechanisms should be used**: To verify user identities, use secure authentication protocols such as [Multi-factor Authentication (MFA)](https://aws.amazon.com/what-is/mfa/). Use robust authorization mechanisms that enforce access controls at the user and resource levels. Review and update user access permissions regularly to reflect changes in roles or responsibilities.
* **Use the [Principle of Least Privilege (PoLP)](https://www.digitalguardian.com/blog/what-principle-least-privilege-polp-best-practice-information-security-and-compliance)**: Follow the PoLP by granting users only the privileges necessary to complete their tasks. Allowing users too many privileges increases the risk of unauthorized access if their accounts are compromised.
* **Direct Object References Should be Protected and Validated**: Avoid exposing internal references to resources directly in URLs or parameters. Instead, use indirect references or tokens that are difficult to manipulate. To prevent unauthorized access, validate and authorize user access to these references.
* **Conduct Regular Security Testing**: Conduct comprehensive security assessments, including penetration testing and vulnerability scanning, to identify potential access control vulnerabilities. Test and validate the effectiveness of access control mechanisms regularly, and address any identified flaws as soon as possible.
* **Use Security Headers and Best Practices**: To improve the security of your web application, use security headers such as [Content Security Policy (CSP)](https://portswigger.net/web-security/cross-site-scripting/content-security-policy), [Cross-Origin Resource Sharing (CORS)](https://portswigger.net/web-security/cors), and [Strict Transport Security (HSTS)](https://). To reduce the risk of access control vulnerabilities, adhere to security best practices, including secure coding guidelines.
* **Maintain Security Patches and Updates**: Maintain the most recent security patches and updates for your web application and underlying frameworks. Vulnerabilities in access control mechanisms can be prevented by applying software vendor-provided fixes and patches.
* **Educate and Train Developers**: Ensure that developers and the development team have received secure coding training and know the risks associated with Broken Access Control. Encourage an organizational security-conscious culture and ongoing education and awareness programs.

Organizations can significantly reduce the likelihood of Broken Access Control vulnerabilities and improve the overall security of their web applications by implementing these preventive measures and incorporating them into the development lifecycle.


## Conclusion
In conclusion, access control is an important aspect of web security, and developers and organizations must implement all necessary safeguards to avoid a breach in access control. Furthermore, by implementing appropriate access control mechanisms, employing security coding practices, and adhering to best practices, the risk of Broken Access Control is reduced, and applications are protected from unauthorized intrusions.