IDOR (Insecure Direct Object Reference) vulnerability is a common and critical web application weakness that occurs when a web application gives you direct access to objects (data) based on input you supply. This weakness allows an attacker to bypass authorization and access resources in the system that they are not supposed to, such as another user’s data, by simply modifying the value of a parameter used to identify an object.
Think of an online application like a company’s internal filing system. Every employee has a valid access badge, but each badge is meant to grant access only to specific folders. An IDOR vulnerability exists when the system checks that you have a badge, but does not verify whether you are permitted to open a particular file. If file records are identified by simple reference numbers, changing that number can allow an employee to view or modify files that belong to other departments or individuals. The system assumes that because you are authenticated then you should be authorized, an assumption that attackers routinely exploit.
What Exactly is an Insecure Direct Object Reference (IDOR)?
An IDOR vulnerability is a type of Broken Access Control flaw (A01:2025). It arises when a web application uses an identifier to directly access an internal object but fails to carry out a proper authorization check to ensure the current user is permitted to access that specific object.
The “identifier” is often a value provided by the user or their browser, such as:
- User identifier used in a URL path, such as: https://someapi.com/users/105
- Order number as a part of a query parameter, e.g. https://yourstore.com/orders?id=3767
- A document identifier that is placed within the body of an API request, noted as {“documentId”: “abc-def-123”}
- A file name requested from a server, such as https://somesite.com/download?file=invoice_1889.pdf
The vulnerability is not due to the use of the identifier itself, but the web app’s failure to verify that the logged-in user has the required rights to access the resource pointed to by that identifier. This gap can result in unauthorized access to sensitive data, compromise of user accounts, and serious regulatory and compliance breaches.
How IDOR Attack Happens: A Step-by-Step Scenario.
The simplistic nature of IDOR exploitation is what makes it a critical vulnerability. As an attacker, you do not need a sophisticated “hacking” tool to exploit it, only your web browser is sufficient.
Let’s consider a web application that allows you to view their past orders.
- Normal and Expected User Action: You log in to your account and click on “order history”. Then you select an order, and the browser navigates to a URL like: https://someecommerce-site.com/viewOrder?orderID=5326, The server correctly verifies that you are logged in and displays the details for your order, 5326.
- Attacker Reconnaissance: An attacker logs in to their own account on the same site and he/she observes this predictable URL structure. They notice the orderID is a sequential number.
- Parameter Manipulation: The attacker simply modifies the orderID parameter in the URL in their browser, changing it to 5326. https://someecommerce-site.com/viewOrder?orderID=5326
- Authorization Bypass: The attacker then submits the modified request. The server’s inherently flawed access control logic checks if the attacker is authenticated (which they are) but the server then fails to check if they are authorized to view order 5326. Because this crucial check is missing, the server processes the request and returns the full order details for another customer.
By repeating this process, the attacker can enumerate thousands of order IDs in order to systematically harvest sensitive customer information, including name, address, and purchase details. A similar attack could be used to alter or delete data if the vulnerability is present in functions such as “update profile” or “cancel order.”
5 Reasons Why IDOR Vulnerabilities Are Dangerous.
- Easy to Exploit: IDOR vulnerabilities are particularly dangerous because they are easy to exploit and can cause significant damage in a short time. Unlike other technical weaknesses that may require advanced tools or deep system access, an IDOR flaw can often be abused by anyone with a basic understanding of how web applications work. In many cases, no malware, fuzzing tools, or exploit code is required, only simple request manipulation.
- Unauthorized Data Exposure: The most immediate risk is unauthorized access to sensitive information. When object-level authorization is missing, attackers can view confidential personal data, financial records, internal documents, or other business-sensitive information belonging to other users. In sectors such as e-commerce, fintech, and healthcare, this can quickly escalate into a large-scale data breach affecting thousands of customers.
- Account Takeover and Privilege Abuse: Beyond exposing data, IDOR vulnerabilities can enable attackers to modify or delete information. If flawed authorization exists in functions such as profile updates or transaction processing, attackers may change user details, cancel transactions, or perform actions on behalf of other users. What appears to be a “read-only” issue can quickly become a serious integrity and availability risk.
- Regulatory and Business Impact: From a business perspective, exploited IDOR vulnerabilities often lead to regulatory violations, especially where data protection laws apply. Unauthorized access to sensitive data can trigger breach disclosures, investigations, fines, and legal consequences. The resulting loss of customer trust can be even more damaging and difficult to recover from.
- Difficult to Detect: IDOR vulnerabilities often remain undetected for long periods because attackers may use valid credentials and legitimate application features. Their activity can blend into normal user behavior, meaning that by the time the issue is discovered, significant damage may already have occurred.
How to Prevent IDOR Vulnerabilities.
Preventing IDOR vulnerability requires a security-first approach at the development stage. You cannot rely on hiding identifiers, as attackers are skillful at finding them.
- Implement Strict, Server-Side Access Control Checks: This is the most crucial defence against an IDOR vulnerability. For every request that accesses a private resource, your web application’s backend must verify that the currently authenticated user has the necessary permissions for that specific resource it is requesting. Never trust user-supplied input without proper verification.
- Bad (Vulnerable) Logic: Is the user logged in? If yes, show them the order details for the orderID they provided.
- Good (Secure) Logic: Is the user logged in? If yes, get the user’s ID from their secure session. Then, check in the database if the order_id they provided actually belongs to their user ID. Only show the details if both conditions are true.
- Use Indirect and Unpredictable Object References: Avoid the use of direct, sequential, or predictable identifiers in URLs and API calls. Instead, use identifiers that are difficult and/or impossible for attackers to guess.
- Use UUIDs: Replace sequential integers (1, 2, 3) with Universally Unique Identifiers (UUIDs) or other long and/or random strings.
- Vulnerable: id=1234
- Secure: id=3er3e9-a556-439b-8232d-0e1f2a2b4c5d
- Conduct Regular Security Testing: It is much better to proactively detect the IDOR vulnerabilities than dealing with a security breach. A thorough Vulnerability Assessment and Penetration Testing (VAPT) engagement by an expert firm like A&DForensics will simulate real-world attacks to uncover and report these and other access control flaws before malicious actors can exploit them.
How Can A&D Forensics Help?
A&D Forensics helps you identify and reduce cybersecurity risks through expert-led Vulnerability Assessment and Penetration Testing (VAPT). We uncover security gaps such as IDOR vulnerabilities, simulate real-world attacks, and provide clear, actionable remediation guidance to strengthen your systems, support compliance, and protect your web applications and business.
Conclusion.
Indirect object reference (IDOR) vulnerabilities may seem simple, but their impact can be very severe when left unchecked. By failing to enforce proper and adequate security measures, namely, authorization at the object level, web applications expose sensitive data and critical functions to unauthorized users. Preventing IDOR vulnerability requires deliberate access control design, consistent server-side validation, and regular security testing. Addressing these weaknesses early not only reduces security and compliance risks but also helps protect user trust and the integrity of the application.
Contributor: Danladi Galadima
