OWASP Top 10 API Security: Broken Object Property Level Authorization

Introduction

APIs are essential for enabling communication and data exchange between different systems. However, the security of APIs is crucial to prevent unauthorized access and data breaches. One vulnerability that poses a significant risk is Broken Object Property Level Authorization. In this article, we will explore the threat agents, attack vectors, security weaknesses, impacts, and preventive measures related to API3:2023 Broken Object Property Level Authorization.

Threat Agents and Attack Vectors

The threat agents in this context are typically users or attackers interacting with the API endpoints. The attack vectors involve manipulating API requests to gain unauthorized access to sensitive object properties or modify their values. Different protocols may require specific techniques, such as crafting requests or using automated tools, to identify and manipulate object properties.

Security Weakness

The security weakness lies in the inadequate validation of user access to specific object properties through API endpoints. APIs may expose sensitive object properties that should not be accessible to users or allow them to change properties they should not have access to. Inspecting API responses and fuzzing techniques can reveal sensitive information and hidden properties. Lack of proper validation can lead to unauthorized access, data disclosure, data loss, data corruption, privilege escalation, or account takeover.

Impacts

Unauthorized access to private or sensitive object properties can result in data exposure, reputational damage, and loss of trust. Unauthorized changes to critical properties may lead to data loss or corruption. Privilege escalation can occur, granting attackers higher levels of access and control. Partial or full account takeover can also pose significant risks to affected users.

Example Attack Scenarios

Scenario #1: Financial Application

An API endpoint in a financial application allows users to retrieve their account balance. However, the endpoint fails to validate the user’s authorization to access other users’ balances. Consider the following API call:

GET /api/account/balance?userId=123456

An attacker can exploit this vulnerability by modifying the userId parameter to access another user’s balance:

GET /api/account/balance?userId=987654

To prevent this, the API should validate that the requesting user has the necessary privileges to access the specified account balance.

Scenario #2: E-commerce Website

An e-commerce website provides an API endpoint for updating a user’s shipping address. However, the endpoint allows users to update any other user’s address without proper authorization. Consider the following API call:

PUT /api/user/address
Content-Type: application/json

{
  "userId": "123456",
  "address": "123 Main St"
}

An attacker can exploit this vulnerability by modifying the userId parameter to update someone else’s address:

PUT /api/user/address
Content-Type: application/json

{
  "userId": "987654",
  "address": "456 Elm St"
}

To prevent this, the API should verify that the requesting user has the permission to update the specified user’s address.

Scenario #3: Social Media Platform

A social media platform allows users to post comments on other users’ profiles. However, the API endpoint fails to enforce proper authorization, allowing any user to post comments on behalf of another user. Consider the following API call:

POST /api/profiles/123456/comments
Content-Type: application/json

{
  "text": "Great profile!"
}

An attacker can exploit this vulnerability by modifying the endpoint to post a comment on a different user’s profile:

POST /api/profiles/987654/comments
Content-Type: application/json

{
  "text": "Hacked profile!"
}

To prevent this, the API should validate that the requesting user has the authority to post comments on the specified user’s profile.

By implementing proper authorization checks and validating user access to specific resources, these vulnerabilities can be mitigated, ensuring the integrity and security of the system.

Prevention Measures

To mitigate the risks associated with Broken Object Property Level Authorization, implement the following preventive measures:

1. Validate Access

Ensure that users have appropriate access to object properties exposed through API endpoints. Only expose properties that users should be able to access based on their privileges.

2. Selective Data Return

Cherry-pick specific properties to return instead of exposing all object properties. Avoid using generic methods that may inadvertently expose sensitive data.

3. Avoid Mass Assignment

Avoid automatically binding client inputs to code variables, internal objects, or object properties. Only allow changes to properties that should be updated by the client, and validate modifications against authorization rules.

4. Schema-Based Response Validation

Implement a schema-based response validation mechanism to enforce the expected data returned by API methods. Define and enforce data structures to ensure consistency and security.

5. Minimum Data Exposure

Keep the returned data structures to the minimum required by the business or functional requirements of the endpoint. Avoid exposing unnecessary information that could pose security risks.

Conclusion

API3:2023 Broken Object Property Level Authorization is a significant vulnerability that can lead to unauthorized access, data breaches, and other detrimental impacts. By understanding the threat agents, attack vectors, security weaknesses, and potential impacts, organizations can take proactive measures to prevent and mitigate these risks. By implementing proper access validation, selective data return, avoiding mass assignment, employing schema-based response validation, and minimizing data exposure, API developers can ensure the security and integrity of their systems, protecting user data and maintaining user trust.

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