IDOR Vulnerability: Explanation, Exploitation, and Prevention

Introduction

In this article, we will explore the Insecure Direct Object Reference (IDOR) vulnerability, a common security vulnerability in web applications that can have significant impacts on data confidentiality, integrity, and availability. We will explain what an IDOR vulnerability is, how it can be exploited, and how to prevent it. We will also provide examples of vulnerable code and methods to exploit IDOR using popular tools such as Burp Suite, wfuzz, and ffuf.

What is IDOR?

Insecure Direct Object Reference (IDOR) is a security vulnerability that occurs when a web application directly exposes references to internal objects, such as files, database records, or primary keys, without properly verifying user permissions. An attacker can exploit this vulnerability to access or modify data they are not authorized to access. IDOR vulnerabilities are common in applications that use primary keys to identify objects, and in applications that use URLs to identify objects.

Vulnerable Code Example

Here is a simple example of code vulnerable to an IDOR attack. In this example, a web application allows a user to view their profile by accessing the URL http://example.com/profile?id=<ID> where <ID> is the user’s ID.

@app.route("/profile")
def get_profile():
    user_id: request.args.get("id")
    user: User.query.get(user_id)
    if user:
        return render_template("profile.html", user=user)
    else:
        return "User not found", 404

In this example, the application directly retrieves the user from the provided ID, without checking if the logged-in user is authorized to access this profile.

IDOR Exploitation

IDOR exploitation can be performed in different ways, including using tools such as Burp Suite, wfuzz, and ffuf. These tools allow testing object ID values to identify information that the user should not have access to. Attackers can also use social engineering techniques to obtain information about internal objects, such as file names or database identifiers.

Using Burp Suite

Burp Suite is a web security analysis tool that can be used to exploit IDOR vulnerabilities. To exploit IDOR with Burp Suite, proceed as follows:

1. Configure your browser to use Burp Suite as a proxy.
2. Navigate to the target website and identify requests containing direct object references.
3. Send these requests to the Burp Intruder tool.
4. In Burp Intruder, configure payload positions for object reference parameters.
5. Use a payload list containing object IDs you want to test, then launch the attack.
6. Analyze the responses to identify those that contain information you should not have access to.

Using wfuzz

Wfuzz is a command-line tool for performing web security testing, including exploiting IDOR vulnerabilities. To exploit IDOR with wfuzz, proceed as follows:

wfuzz -c -z range,1-100 -X GET "http://example.com/profile?id=FUZZ" --hc 404

In this example, wfuzz tests ID values from 1 to 100 and displays responses that do not return an HTTP status code 404.

Using ffuf

Ffuf (Fuzz Faster U Fool) is a fast and performant command-line tool for performing web security testing, including exploiting IDOR vulnerabilities. To exploit IDOR with ffuf, proceed as follows:

ffuf -u "http://example.com/profile?id=FUZZ" -c -w id_list.txt -fc 404

In this example, ffuf uses an id_list.txt file containing a list of object IDs to test and displays responses that do not return an HTTP status code 404.

Impact

Successful exploitation of an IDOR vulnerability can have several impacts, including:

• Unauthorized access to sensitive information: An attacker can access other users’ data, such as profile information, transaction history, or private documents.
• Unauthorized data modification: An attacker can modify other users’ data, such as profile settings, passwords, or authorization levels.
• Unauthorized data deletion: An attacker can delete other users’ data, resulting in data loss and potential service interruption.

Prevention

To prevent IDOR vulnerabilities, it is important to implement appropriate access controls and systematically verify user permissions. Here are some measures developers can take to prevent IDOR vulnerabilities:

• Use indirect identifiers for objects: Rather than directly exposing primary keys or database identifiers, use indirect identifiers that are securely mapped to internal objects.
• Implement role-based access control: Define clear roles and permissions for users and ensure that access controls are applied consistently throughout the application.
• Systematically verify user permissions: For each action involving an internal object, verify if the logged-in user is authorized to access or modify that object.
• Use proven security mechanisms: Leverage development frameworks and libraries that provide built-in security mechanisms to prevent IDOR vulnerabilities.

Conclusion

In summary, IDOR is a common security vulnerability in web applications that can have significant impacts on data confidentiality, integrity, and availability. Developers must be aware of this vulnerability and implement appropriate access controls to protect web applications against IDOR attacks.