What Is Insecure Direct Object Reference (IDOR)?
Insecure direct object references (IDOR) is a web application security vulnerability that occurs when an application exposes internal object identifiers, such as database keys or file paths, to users without proper access controls.
It can enable attackers to manipulate these identifiers and gain unauthorized access to sensitive data or perform unauthorized actions on the system. IDOR vulnerabilities arise due to inadequate validation and authorization checks on user-supplied input, which may allow malicious users to bypass intended access restrictions.
This is part of a series of articles about cyber attacks.
How IDOR Attacks Happen
IDOR attacks happen when an attacker takes advantage of insufficient access controls and insecure handling of object references in a web application. Here’s a step-by-step breakdown of how an IDOR attack might occur.
- Discovery: The attacker first identifies a vulnerable web application that uses direct object references, such as database keys or file paths, in its URLs or request parameters.
- Analysis: The attacker carefully analyzes the application’s behavior, looking for patterns in the object references and attempting to understand the underlying structure or naming conventions.
- Tampering: Once the attacker has gathered enough information, they modify the object reference in the URL or request parameter, replacing it with a reference to a different object they’re not authorized to access.
- Exploitation: If the application fails to validate and authorize the modified object reference properly, the attacker gains unauthorized access to the targeted resource, such as sensitive data or privileged functions.
After carrying out these steps, the attacker may repeat the process, exploring and exploiting other vulnerable object references within the application, potentially gaining access to additional sensitive data or system functionalities.
Types of IDOR Attacks
URL Tampering
In this type of IDOR attack, the attacker manipulates the object reference directly in the URL. Web applications often include object identifiers, such as database keys or file paths, in the URL to retrieve specific resources.
By altering these identifiers, the attacker attempts to gain unauthorized access to sensitive data or perform restricted actions. URL tampering may involve incrementing or decrementing numerical IDs, substituting alternative strings, or guessing hidden URLs.
Body Manipulation
In this type of attack, the attacker alters the object reference within the HTTP request body, rather than the URL. This often occurs in applications that use POST or PUT methods, where data is sent within the request body rather than as part of the URL. The attacker modifies the object identifier to target unauthorized resources, potentially leading to unauthorized data access or modification.
Cookie or JSON ID Manipulation
Some web applications store object references in cookies or JSON Web Tokens (JWTs) for session management or user authentication purposes. In this type of IDOR attack, the attacker manipulates these stored identifiers to target unauthorized resources. This can involve decoding and altering the value of a JWT or modifying the object reference stored in a cookie before sending it back to the server.
Path Traversal
Path traversal, also known as directory traversal, occurs when the attacker manipulates file paths within a web application to access unauthorized files or directories. This often occurs when the application fails to validate and sanitize user-supplied input used to construct file paths.
The attacker may use special characters, such as “../” (dot-dot-slash), to traverse the file system and access sensitive files, such as configuration files or source code, which can lead to information disclosure or further exploitation.
Best Practices to Prevent IDOR Vulnerabilities
To prevent IDOR vulnerabilities, developers should follow best practices that help ensure the security of their web applications. Some of these best practices include:
Perform User Request Validation
Validating and sanitizing user-supplied input is crucial in preventing IDOR vulnerabilities. Developers should check that input data is in the expected format, and remove any unexpected characters or values. It is also important to perform server-side validation, as client-side validation can be bypassed by a determined attacker.
Authorization checks should be implemented to ensure that the user making the request has the necessary permissions to access the requested resource. It’s essential to verify that the authenticated user has the right to access or perform actions on the targeted object. This should be done for every request, not just at the initial authentication stage, as attackers may try to bypass these controls using various techniques.
Use Indirect Object Reference Maps
Indirect object reference maps can help protect against IDOR vulnerabilities by decoupling user-supplied identifiers from the internal object references used by the application. Instead of directly exposing internal identifiers, such as database keys or file paths, the application associates user-specific tokens or indexes with the actual object references.
For example, when a user logs in, the application could create a temporary mapping between a user-specific index (e.g., 1, 2, 3) and the actual internal object reference (e.g., database key or file path).
This mapping should be stored in the user’s session, and the application should only reference objects using the user-specific index. This way, even if an attacker attempts to manipulate the object reference, they will only be able to access resources within their authorized scope.
Avoid Predictable References
Using predictable references for internal objects, such as sequential numbers or easily guessable strings, can make it easier for attackers to exploit IDOR vulnerabilities. To minimize this risk, developers should use hard-to-guess identifiers, such as universally unique identifiers (UUIDs) or randomized strings.
Additionally, it’s essential to avoid exposing sensitive information in URLs or request parameters. For example, instead of including a user’s email address or other personally identifiable information (PII) in a URL, consider using a unique, non-guessable token that represents the user.
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