Understanding and Detecting IDOR Vulnerabilities

APIs are the connective tissue of modern applications, enabling seamless data exchange and functionality. However, this connectivity also presents potential security risks. One of the most common and potentially damaging vulnerabilities found in APIs is the Insecure Direct Object Reference (IDOR). Often listed in the OWASP Top 10, understanding and mitigating IDOR is crucial for protecting your application and user data.

This post will break down what IDOR is, how attackers exploit it specifically in APIs, and how you can leverage Aikido Security's API scanning capabilities to detect it proactively.

What Exactly is an IDOR?

Imagine you live in an apartment building. Your key (authentication) lets you into the main entrance and your apartment (e.g., #101). An IDOR vulnerability is like having a system where knowing an apartment number (like #102) is enough to let you unlock that door, even though your key is only for #101.

In technical terms, IDOR occurs when an application uses an identifier for direct access to an internal object (like a database record, file, or user profile) but fails to perform proper authorization checks to ensure the current user is actually allowed to access that specific object.

The "identifier" is often something supplied by the user/client, such as:

• A user ID in a URL path (/api/users/12345)

• An order ID in a query parameter (/api/orders?id=9876)

• A document ID in a request body ({"documentId": "abc-def"})

The vulnerability isn't the use of the identifier itself, but the lack of verification that the logged-in user has the rights to access the resource pointed to by that identifier.

Why is IDOR Dangerous, Especially in APIs?

APIs often expose core application functionality and data. An IDOR vulnerability in an API can lead to:

1. Data Breaches: Attackers can iterate through identifiers (e.g., changing /api/users/101 to /api/users/102, /api/users/103, etc.) to access sensitive information belonging to other users (personal details, financial data, private messages).

2. Unauthorized Actions: Attackers might be able to modify or delete data belonging to others by manipulating identifiers in PUT, POST, or DELETE requests (e.g., changing /api/orders/555 to /api/orders/556 in a delete request).

3. Privilege Escalation: In some cases, accessing another user's data or settings might indirectly grant higher privileges.

4. Business Logic Flaws: IDOR can disrupt business processes by allowing unauthorized interaction with resources like invoices, reports, or system configurations.

How Attackers Exploit IDOR via API Scanning

Attackers often use automated tools or simple scripts to probe APIs for IDOR vulnerabilities. The process generally involves:

1. Discovery: Identifying API endpoints that seem to use identifiers (often numerical or predictable strings) in paths, parameters, or request bodies. This is often done by analyzing legitimate application traffic or API documentation (like OpenAPI/Swagger specs).

2. Authentication: Obtaining valid credentials for a low-privileged user account.

3. Manipulation: Systematically changing the identified identifiers in API requests. They might increment/decrement numbers, try common patterns, or substitute known IDs from other contexts.

4. Analysis: Examining the API responses. If a request with a manipulated identifier returns data or confirms an action related to another user's resources, an IDOR vulnerability likely exists.

Detecting IDOR with Aikido Security's API Scanning (DAST)

Manually testing for IDOR across complex APIs is tedious and error-prone. This is where automated Dynamic Application Security Testing (DAST) tools like Aikido Security come in. Aikido's API scanning feature can automatically probe your API endpoints for IDOR vulnerabilities.

Here’s how it generally works:

1. Understanding the API: Aikido needs to know your API structure. You provide this typically via an OpenAPI (Swagger) specification file or by using Zen Firewall to automatically map out your API.

2. Authenticated Scanning: IDOR testing is most effective when performed from the perspective of an authenticated user. Aikido needs credentials to log in as a test user. This allows it to make requests as that user.

3. Identifier Identification: Aikido intelligently analyzes the API specification to identify potential direct object reference parameters (like userId, orderId, id, etc.).

4. Intrusion Attempts: Aikido makes requests to the identified endpoints using the provided authentication. It then systematically substitutes the identified parameters with different values (e.g., values that might belong to other test users if configured, or simply trying sequential/common IDs).

5. Response Analysis: Aikido examines the responses to these modified requests. If it receives data it shouldn't (based on the logged-in test user's permissions) or if an action succeeds improperly, it flags a potential IDOR vulnerability.

Setting Up API Scanning for IDOR Detection in Aikido

Configuring Aikido to scan your API for IDOR is straightforward:

1. Navigate to Domains and API’s: Log in to your Aikido Security dashboard and go to the Domains and API’s section.

2. Add or configure a domain: Define the target application you want to scan. This usually involves providing the base URL, providing an OpenAPI spec, or linking to an existing Zen Firewall application.

3. Configure Authentication (Crucial for IDOR):

   • Go to the Authentication settings for your DAST target.

   • Select the appropriate authentication method used by your API (e.g., Login via form, Custom Headers, OAuth, Basic auth).

   • Provide valid credentials for the main user account.

   • Provide valid credentials for a test user account. This allows Aikido to explicitly test if User A can access User B's resources by using User B's known IDs.

   • It's critical that both users exists and can log in. Why? Aikido needs to act as this user to test if they can access resources belonging to other users by manipulating IDs.

4. Enhance route information with Aikido AI by going to Routes clicking actions and “Enhance OpenAPI spec”

   

5. Run the Scan: Initiate the API scan.

Beyond Detection: Preventing IDOR

While Aikido is excellent for detecting IDOR, prevention requires secure coding practices:

1. Implement Strong Authorization: This is the most critical defense. For every request that accesses a resource via an identifier, verify on the server-side that the currently authenticated user has the necessary permissions to access or modify that specific resource. Don't rely solely on the ID provided by the client.

2. Avoid Direct, Guessable IDs: Where possible, use less predictable identifiers like UUIDs (Universally Unique Identifiers) instead of sequential integers (1, 2, 3). However, remember that even with UUIDs, the authorization check (Step 1) is still mandatory, as UUIDs can still leak or be discovered.

3. Use Indirect References (Mapping): Consider using session-based references or mapping internal IDs to per-user/per-session temporary IDs. This adds a layer of abstraction. Again, server-side authorization remains essential.

Conclusion

IDOR remains a prevalent and dangerous vulnerability in web applications and especially APIs. Attackers can exploit it to gain unauthorized access to sensitive data and functionality. By understanding how IDOR works and leveraging automated tools like Aikido Security's API scanning with proper authentication configured, you can proactively identify these weaknesses in your APIs before attackers do. Remember that detection is only part of the solution; robust server-side authorization checks are the ultimate key to preventing IDOR. Stay vigilant, scan regularly, and build secure APIs!