IDOR (Insecure Direct Object References) Vulnerability - Detailed Analysis

IDOR (Insecure Direct Object References) is a security vulnerability in web applications where a user can access or modify another user's data due to a lack of access control. In this article, we will explain all aspects of the IDOR vulnerability in detail.

1. What is IDOR?

IDOR vulnerabilities occur in web applications that use direct object references. These applications often provide access to data objects via URL parameters or form data. If these references are processed without validation, malicious users can access unauthorized data.

For example:

https://example.com/user/profile?user_id=123

Here, the user_id parameter determines the profile information. If the application only checks the user_id without verifying access permissions, an attacker can access other users' information by changing the user_id value.

2. Basic Structure of IDOR Vulnerability

IDOR vulnerabilities generally arise from two main reasons:

• Access Control Issues: Users may be able to access other users' data when they should only have access to their own data.
• Authorization Issues: Users may perform actions they are not authorized for, bypassing proper authorization checks.

3. Types of IDOR

3.1. Access Control Issues

Access control issues typically occur when the application does not properly enforce access restrictions to the data set a user is authorized to access, allowing access to other users' data.

3.2. Authorization Issues

Authorization issues allow users to view or modify not only their own data but also others'. This occurs when the application fails to properly check user permissions.

4. IDOR Attack Techniques

4.1. Simple IDOR Attacks

These attacks are often carried out by modifying URL or form parameters. In simple IDOR attacks, the attacker usually changes the parameters in the URL.

Example Scenario:

https://example.com/profile?user_id=1001

An attacker might change the user_id parameter to:

https://example.com/profile?user_id=1002

to access another user's profile information.

4.2. IDOR in Database Queries

This attack type involves object references used in database queries. If ID values used in database queries are not properly validated, attackers can gain unauthorized access to data.

Example Scenario:

https://example.com/orders/details?order_id=987

An attacker might change the order_id parameter to:

https://example.com/orders/details?order_id=988

to access another user's order details.

4.3. IDOR in File Access

IDOR attacks in file access typically occur when file references are not properly checked. In these attacks, attackers can gain unauthorized access to files.

Example Scenario:

https://example.com/download?file_id=xyz123

An attacker might change the file_id parameter to:

https://example.com/download?file_id=xyz124

to access unauthorized files.

5. Detecting and Preventing IDOR Vulnerabilities

5.1. Detection Methods

• Manual Testing: Test access control by modifying URL and form parameters. Check for unauthorized access by testing with different user accounts. For example, test access limits by trying different user_id values.
• Automated Tools: Use security scanners and penetration testing tools to detect IDOR vulnerabilities. These tools perform automated tests on specific parameters to identify vulnerabilities.

5.2. Prevention Methods

• Access Control: Check if the user is authorized for each access request. Implement comprehensive authorization checks before granting access to data. This ensures that users can only access their own data.
• Secure Reference Usage: Use secure references for objects that require access control. Prevent users from manipulating object identities directly. For example, use encrypted or anonymized references instead of directly specifying file references in the URL.
• Security Testing: Regularly subject your application to security testing to detect IDOR and other vulnerabilities. Penetration testing is an effective way to identify potential security issues.

6. Example Application

User Profile Access

Profile View:

https://example.com/profile/view?user_id=123

Attack Scenario: A user changes the user_id value and views another user's profile information.

Code Example (PHP)

In a simple IDOR example, we fetch data using the user_id parameter directly from the user. This method has weak access control and is vulnerable to IDOR attacks.

<?php
// Simple IDOR example
$user_id = $_GET['user_id']; // ID parameter from the user
// Fetching data without checking user authorization
$sql = "SELECT * FROM users WHERE id = $user_id";
?>

The code above does not check if the user is authorized to access their own data. It returns data for any user_id value provided.

A secure IDOR prevention strategy should ensure that the user can only access their own data. The following code enforces this access control:

<?php
// Secure IDOR example with access control
session_start();
$user_id = $_GET['user_id'];

// Check user authorization
if ($_SESSION['user_id'] == $user_id) {
    // Allow user to view their own data
    $sql = "SELECT * FROM users WHERE id = $user_id";
} else {
    // Unauthorized access, error message
    echo "Unauthorized access!";
}
?>

In this code, $_SESSION['user_id'] is used to check the user's authorization, allowing access only to their own data. Unauthorized users receive an "Unauthorized access!" message.

IDOR vulnerabilities can pose serious security risks in web applications. By rigorously implementing access and authorization controls and performing regular security testing, you can protect against such vulnerabilities.